Data transfer control device and electronic instrument

ABSTRACT

A data transfer control device includes an OUT-transfer transmitter circuit which transmits OUT data by driving a serial signal line, a clock-transfer transmitter circuit which transmits a clock signal CLK by driving a serial signal line, a PLL circuit which generates the clock signal CLK, and a power-down setting circuit which sets a power-down mode. In a first power-down mode, the OUT-transfer transmitter circuit is set to the power-down mode, and the clock-transfer transmitter circuit is set to the power-down mode to stop a system clock signal of a target-side data transfer control device. In a second power-down mode, the OUT-transfer transmitter circuit is set to the power-down mode without setting the clock-transfer transmitter circuit to the power-down mode.

This is a Divisional of application Ser. No. 10/934,461, now U.S. Pat.No. 7,249,271, filed Sep. 7, 2004. The disclosure of the priorapplication is hereby incorporated by reference herein in its entirety.

Japanese Patent Application No. 2003-314055, filed on Sep. 5, 2003,Japanese Patent Application No. 2003-314056, filed on Sep. 5, 2003,Japanese Patent Application No. 2004-14412, filed on Jan. 22, 2004,Japanese Patent Application No. 2004-14413, filed on Jan. 22, 2004, andJapanese Patent Application No. 2004-65937, filed on Mar. 9, 2004, arehereby incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

The present invention relates to a data transfer control device and anelectronic instrument.

In recent years, a high-speed serial transfer interface such as lowvoltage differential signaling (LVDS) has attracted attention as aninterface standard aiming at reducing EMI noise or the like. In thehigh-speed serial transfer interface, data transfer is realized byallowing a transmitter circuit to transmit serialized data usingdifferential signals and a receiver circuit to differentially amplifythe differential signals. Japanese Patent Application Laid-open No.2002-314397 and Japanese Patent Application Laid-open No. 2003-218843have disclosed a conventional technology relating to the high-speedserial transfer interface, for example.

However, since the high-speed serial transfer interface allows currentto constantly flow through the transmitter circuit and the receivercircuit, reduction of power consumption is limited. On the other hand,data transfer cannot be performed if the path of the constant current iscut. Therefore, the technical subject is to realize an effectivepower-down mode in the transmitter circuit and the receiver circuitconforming to the high-speed serial transfer interface.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention relates to a host-side data transfercontrol device which performs data transfer with a target-side datatransfer control device, the host-side data transfer control deviceincluding:

an OUT-transfer transmitter circuit which is connected with anOUT-transfer receiver circuit of the target-side data transfer controldevice through an OUT-transfer serial signal line, and transmits OUTdata by driving the OUT-transfer serial signal line;

a clock-transfer transmitter circuit which is connected with aclock-transfer receiver circuit of the target-side data transfer controldevice through a clock-transfer serial signal line, and transmits aclock signal, which is used to sample the OUT data and is used togenerate a system clock signal of the target-side data transfer controldevice, by driving the clock-transfer serial signal line; and

a power-down setting circuit for setting a power-down mode whichincludes a first power-down mode and a second power down mode,

wherein, in the first power-down mode, the power-down setting circuitsets the OUT-transfer transmitter circuit to the power-down mode andsets the clock-transfer transmitter circuit to the power-down mode tostop the system clock signal of the target-side data transfer controldevice, and, in the second power-down mode, the power-down settingcircuit sets the OUT-transfer transmitter circuit to the power-down modewithout setting the clock-transfer transmitter circuit to the power-downmode.

Another aspect of the present invention relates to a host-side datatransfer control device which performs data transfer with a target-sidedata transfer control device, the host-side data transfer control deviceincluding:

an OUT-transfer transmitter circuit which is connected with anOUT-transfer receiver circuit of the target-side data transfer controldevice through an OUT-transfer serial signal line, and transmits OUTdata by driving the OUT-transfer serial signal line;

a clock-transfer transmitter circuit which is connected with aclock-transfer receiver circuit of the target-side data transfer controldevice through a clock-transfer serial signal line, and transmits aclock signal, which is used to sample the OUT data and is used togenerate a system clock signal of the target-side data transfer controldevice, by driving the clock-transfer serial signal line;

an IN-transfer receiver circuit which is connected with an IN-transfertransmitter circuit of the target-side data transfer control devicethrough an IN-transfer serial signal line, and receives IN data; and

a strobe-transfer receiver circuit which is connected with astrobe-transfer transmitter circuit of the target-side data transfercontrol device through a strobe-transfer serial signal line, andreceives a strobe for sampling the IN data,

wherein the strobe-transfer receiver circuit receives the strobe fromthe strobe-transfer transmitter circuit of the target-side data transfercontrol device, the strobe being generated by the target-side datatransfer control device based on the clock signal transmitted by theclock-transfer transmitter circuit of the host-side data transfercontrol device.

A further aspect of the present invention relates to a target-side datatransfer control device which performs data transfer with a host-sidedata transfer control device, the target-side data transfer controldevice including:

an OUT-transfer receiver circuit which is connected with an OUT-transfertransmitter circuit of the host-side data transfer control devicethrough an OUT-transfer serial signal line, and receives OUT data;

a clock-transfer receiver circuit which is connected with aclock-transfer transmitter circuit of the host-side data transfercontrol device through a clock-transfer serial signal line, and receivesa clock signal which is used to sample the OUT data and is used togenerate a system clock signal of the target-side data transfer controldevice;

an IN-transfer transmitter circuit which is connected with anIN-transfer receiver circuit of the host-side data transfer controldevice through an IN-transfer serial signal line, and transmits IN databy driving the IN-transfer serial signal line; and

a strobe-transfer transmitter circuit which is connected with astrobe-transfer receiver circuit of the host-side data transfer controldevice through a strobe-transfer serial signal line, and transmits astrobe for sampling the IN data by driving the strobe-transfer serialsignal line,

wherein the strobe-transfer transmitter circuit transmits the strobegenerated based on the clock signal received by the clock-transferreceiver circuit to the strobe-transfer receiver circuit of thehost-side data transfer control device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a configuration example of a data transfer control device.

FIGS. 2A and 2B are illustrative of a normal operation and a firstpower-down mode M1.

FIGS. 3A and 3B are illustrative of second and third power-down modes M1and M2.

FIG. 4 is illustrative of power-down mode setting.

FIG. 5 is a configuration example of a strobe control circuit.

FIG. 6 is illustrative of asynchronous transfer.

FIG. 7 is a configuration example of a transmitter circuit and areceiver circuit.

FIG. 8 is a detailed first configuration example of a transmittercircuit and a receiver circuit.

FIG. 9 is a comparative example of a transmitter circuit and a receivercircuit.

FIG. 10 is a waveform diagram illustrating an operation in the firstconfiguration example.

FIG. 11 is another waveform diagram illustrating an operation in thefirst configuration example.

FIGS. 12A, 12B, and 12C are illustrative of a method using a specialcode.

FIGS. 13A and 13B are illustrative of a method for setting or cancelinga clock-transfer power-down mode.

FIG. 14 is illustrative of a power-down control method in an embodimentof the present invention.

FIG. 15 is illustrative of a power-down control method in an embodimentof the present invention.

FIG. 16 is a detailed second configuration example of a transmittercircuit and a receiver circuit.

FIG. 17 is a waveform diagram illustrating an operation in the secondconfiguration example.

FIG. 18 is another waveform diagram illustrating an operation in thesecond configuration example.

FIG. 19 is a detailed third configuration example of a transmittercircuit and a receiver circuit.

FIGS. 20A, 20B, and 20C are detailed examples of an inverter circuit.

FIG. 21 is a configuration example of an electronic instrument.

DETAILED DESCRIPTION OF THE EMBODIMENT

Embodiments of the present invention are described below.

One embodiment of the present invention provides a host-side datatransfer control device which performs data transfer with a target-sidedata transfer control device, the host-side data transfer control deviceincluding:

an OUT-transfer transmitter circuit which is connected with anOUT-transfer receiver circuit of the target-side data transfer controldevice through an OUT-transfer serial signal line, and transmits OUTdata by driving the OUT-transfer serial signal line;

a clock-transfer transmitter circuit which is connected with aclock-transfer receiver circuit of the target-side data transfer controldevice through a clock-transfer serial signal line, and transmits aclock signal, which is used to sample the OUT data and is used togenerate a system clock signal of the target-side data transfer controldevice, by driving the clock-transfer serial signal line; and

a power-down setting circuit for setting a power-down mode whichincludes a first power-down mode and a second power down mode,

wherein, in the first power-down mode, the power-down setting circuitsets the OUT-transfer transmitter circuit to the power-down mode andsets the clock-transfer transmitter circuit to the power-down mode tostop the system clock signal of the target-side data transfer controldevice, and, in the second power-down mode, the power-down settingcircuit sets the OUT-transfer transmitter circuit to the power-down modewithout setting the clock-transfer transmitter circuit to the power-downmode.

According to this embodiment, in the first power-down mode, theclock-transfer transmitter circuit is set to the power-down mode, andthe system clock signal of the target-side data transfer control devicestops. Therefore, the target-side data transfer control device can beset to the power-down mode without performing complicated control. Inthe second power-down mode, the clock-transfer transmitter circuit isnot set to the power-down mode, and the OUT-transfer transmitter circuitis set to the power-down mode. A reduction of power consumption can beachieved by setting the OUT-transfer transmitter circuit to thepower-down mode. Moreover, the system clock signal of the target-sidedata transfer control device is not stopped by not setting theclock-transfer transmitter circuit to the power-down mode. Therefore,the target can appropriately take action against the host, whereby aminute and intelligent power-down control can be realized.

This data transfer control device may include;

an IN-transfer receiver circuit which is connected with an IN-transfertransmitter circuit of the target-side data transfer control devicethrough an IN-transfer serial signal line, and receives IN data; and

a strobe-transfer receiver circuit which is connected with astrobe-transfer transmitter circuit of the target-side data transfercontrol device through a strobe-transfer serial signal line, andreceives a strobe for sampling the IN data, and

in the first power-down mode, the power-down setting circuit may set theOUT-transfer transmitter circuit, the clock-transfer transmittercircuit, the IN-transfer receiver circuit, and the strobe-transferreceiver circuit to the power-down mode, and, in the second power-downmode, the power-down setting circuit may set the OUT-transfertransmitter circuit, the IN-transfer receiver circuit, and thestrobe-transfer receiver circuit to the power-down mode without settingthe clock-transfer transmitter circuit to the power-down mode.

This enables a minute power-down control to be performed while realizinga full-duplex transfer.

This data transfer control device may include:

an IN-transfer receiver circuit which is connected with an IN-transfertransmitter circuit of the target-side data transfer control devicethrough an IN-transfer serial signal line, and receives IN data; and

a strobe-transfer receiver circuit which is connected with astrobe-transfer transmitter circuit of the target-side data transfercontrol device through a strobe-transfer serial signal line, andreceives a strobe for sampling the IN data, and

the power-down mode may include a third power-down mode, and in thethird power-down mode, the power-down setting circuit may set theIN-transfer receiver circuit and the strobe-transfer receiver circuit tothe power-down mode without setting the OUT-transfer transmitter circuitand the clock-transfer transmitter circuit to the power-down mode.

This enables the circuit which need not operate in the full-duplextransfer to be set to the power-down mode, whereby power consumption canbe reduced.

With this data transfer control device, the strobe-transfer receivercircuit may receive the strobe from the strobe-transfer transmittercircuit of the target-side data transfer control device, the strobebeing generated by the target-side data transfer control device based onthe clock signal transmitted by the clock-transfer transmitter circuit.

According to this feature, since the vibration frequencies of the clocksignal and the strobe become the same, a phase adjustment circuit with acomplicated configuration or the like for sampling becomes unnecessary,whereby a reduction of power consumption and circuit scale can beachieved.

With this data transfer control device, at least one of the OUT-transfertransmitter circuit and the clock-transfer transmitter circuit transmitsa power-down command to a receiver which is one of the OUT-transferreceiver circuit and the clock-transfer receiver circuit of thetarget-side data transfer control device for setting the receiver to thepower-down mode by current-driving a serial signal line which is one ofthe OUT-transfer serial signal line and the clock-transfer serial signalline using a current driver in a normal transfer mode.

This makes it unnecessary to provide a signal line for transferring thepower-down command separately from the serial signal line. As a result,the circuit scale can be reduced while realizing a reduction of powerconsumption.

With this data transfer control device, the OUT-transfer transmittercircuit may transmit the power-down command for setting the OUT-transferreceiver circuit and the clock-transfer receiver circuit of thetarget-side data transfer control device to the power-down mode bycurrent-driving the OUT-transfer serial signal line using the currentdriver in the normal transfer mode.

With this data transfer control device, at least one of the OUT-transfertransmitter circuit and the clock-transfer transmitter circuit transmitsa special code as the power-down command, the special code beingobtained by using an encoding method which expands a bit width.

With this data transfer control device, at least one of the OUT-transfertransmitter circuit and the clock-transfer transmitter circuit includesa current driver and a voltage driver, the current drivercurrent-driving a serial signal line which is one of the OUT-transferserial signal line and the clock-transfer serial signal line, thevoltage driver electrically disconnecting from the serial signal line ina normal transfer mode, and the voltage driver electrically connectingwith the serial signal line and voltage-driving the serial signal linein the power-down mode, and

wherein the voltage driver outputs a power-down voltage or a wakeupvoltage to the serial signal line, the power-down voltage being used forsetting a receiver which is one of the OUT-transfer receiver circuit andthe clock-transfer receiver circuit of the target-side data transfercontrol device to the power-down mode, and the wakeup voltage being usedfor canceling the power-down mode of the receiver circuit.

This makes it unnecessary to provide a signal line for transferring thepower-down voltage or the wakeup voltage separately from the serialsignal line, whereby a reduction of the circuit scale and facilitationof mounting can be achieved.

Another embodiment of the present invention provides a host-side datatransfer control device which performs data transfer with a target-sidedata transfer control device, the host-side data transfer control deviceincluding:

an OUT-transfer transmitter circuit which is connected with anOUT-transfer receiver circuit of the target-side data transfer controldevice through an OUT-transfer serial signal line, and transmits OUTdata by driving the OUT-transfer serial signal line;

a clock-transfer transmitter circuit which is connected with aclock-transfer receiver circuit of the target-side data transfer controldevice through a clock-transfer serial signal line, and transmits aclock signal, which is used to sample the OUT data and is used togenerate a system clock signal of the target-side data transfer controldevice, by driving the clock-transfer serial signal line;

an IN-transfer receiver circuit which is connected with an IN-transfertransmitter circuit of the target-side data transfer control devicethrough an IN-transfer serial signal line, and receives IN data; and

a strobe-transfer receiver circuit which is connected with astrobe-transfer transmitter circuit of the target-side data transfercontrol device through a strobe-transfer serial signal line, andreceives a strobe for sampling the IN data,

wherein the strobe-transfer receiver circuit receives the strobe fromthe strobe-transfer transmitter circuit of the target-side data transfercontrol device, the strobe being generated by the target-side datatransfer control device based on the clock signal transmitted by theclock-transfer transmitter circuit of the host-side data transfercontrol device.

According to this embodiment, a full-duplex transfer can be realized.Moreover, since the vibration frequencies of the clock signal and thestrobe become the same, a phase adjustment circuit with a complicatedconfiguration or the like for sampling becomes unnecessary, whereby areduction of power consumption and circuit scale can be achieved.

This data transfer control device may include a serial/parallelconversion circuit which samples the IN data received by the IN-transferreceiver circuit based on the strobe received by the strobe-transferreceiver circuit, converts serial data obtained by sampling the IN datainto parallel data, and outputs the converted parallel data, and

the serial/parallel conversion circuit may asynchronously transfer theparallel data to a logic circuit in a subsequent stage which operates insynchronization with the clock signal.

This enables an asynchronous transfer to be performed through a path ata low transfer rate, whereby a stable asynchronous transfer can berealized.

A further embodiment of the present invention provides a target-sidedata transfer control device which performs data transfer with ahost-side data transfer control device, the target-side data transfercontrol device including:

an OUT-transfer receiver circuit which is connected with an OUT-transfertransmitter circuit of the host-side data transfer control devicethrough an OUT-transfer serial signal line, and receives OUT data;

a clock-transfer receiver circuit which is connected with aclock-transfer transmitter circuit of the host-side data transfercontrol device through a clock-transfer serial signal line, and receivesa clock signal which is used to sample the OUT data and is used togenerate a system clock signal of the target-side data transfer controldevice;

an IN-transfer transmitter circuit which is connected with anIN-transfer receiver circuit of the host-side data transfer controldevice through an IN-transfer serial signal line, and transmits IN databy driving the IN-transfer serial signal line; and

a strobe-transfer transmitter circuit which is connected with astrobe-transfer receiver circuit of the host-side data transfer controldevice through a strobe-transfer serial signal line, and transmits astrobe for sampling the IN data by driving the strobe-transfer serialsignal line,

wherein the strobe-transfer transmitter circuit transmits the strobegenerated based on the clock signal received by the clock-transferreceiver circuit to the strobe-transfer receiver circuit of thehost-side data transfer control device.

According to this embodiment, a full-duplex transfer can be realized.Moreover, since it is unnecessary to provide a clock generation circuitin the target-side data transfer control device, a reduction of powerconsumption and circuit scale can be achieved.

This data transfer control device may include a strobe control circuitwhich receives the clock signal received by the clock-transfer receivercircuit, and outputs the strobe to the strobe-transfer transmittercircuit by performing strobe control.

This data transfer control device may include a frequency dividercircuit which receives the clock signal received by the clock-transferreceiver circuit, and generates the system clock signal of thetarget-side data transfer control device.

A still further embodiment of the present invention provides anelectronic instrument including one of the above data transfer controldevices and at least one of a communication device, a processor, animaging device, and a display device.

Embodiments of the present invention are described below in detail. Notethat the embodiments described hereunder do not in any way limit thescope of the invention defined by the claims laid out herein. Note alsothat not all of the elements of these embodiments should be taken asessential requirements to the means of the present invention.

1. Configuration Example of Data Transfer Control Device

FIG. 1 shows a configuration example of host-side and target-side datatransfer control devices 10 and 30. In this embodiment, a bridgefunction between a system bus and an interface bus is realized by usingthe host-side and target-side data transfer control devices 10 and 30.The data transfer control devices 10 and 30 are not limited to theconfiguration shown in FIG. 1. Some of the circuit blocks shown in FIG.1 may be omitted, or the connection configuration between the circuitblocks may be changed, or a circuit block differing from those shown inFIG. 1 may be added. A configuration in which at least one of linkcontrollers 200 and 300 and interface circuits 210 and 310 is omittedmay be employed.

The host (TX) side data transfer control device 10 and the target (RX)side data transfer control device 30 transfer packets through a serialbus for differential signals, for example. In more detail, the host-sidedata transfer control device 10 and the target-side data transfercontrol device 30 transmit or receive a packet by current-driving (orvoltage-driving) differential signal lines (serial signal lines in abroad sense; hereinafter the same) of the serial bus.

The host-side data transfer control device 10 includes an interfacecircuit 210 which performs interface processing between the datatransfer control device 10 and a system device such as a CPU and adisplay controller. The interface circuit 210 realizes an RGB interface,MPU interface, or serial interface between the data transfer controldevice 10 and the system device.

The host-side data transfer control device 10 includes the linkcontroller 200 which performs link layer processing (packet generation,packet analysis, transaction control, and the like). The link controller200 performs processing of generating a packet (request packet, streampacket, and the like) transferred to the target-side data transfercontrol device 30 through the serial bus, and transmitting the generatedpacket. In more detail, the link controller 200 starts a transmissiontransaction and directs a transceiver 20 to transmit the generatedpacket.

The host-side data transfer control device 10 includes the transceiver20 (serial interface circuit) which performs physical layer processingor the like. The transceiver 20 transmits a packet indicated by the linkcontroller 200 to the target-side data transfer control device 30through the serial bus. The transceiver 20 receives a packet from thetarget-side data transfer control device 30. In this case, the linkcontroller 200 analyzes the received packet and performs the link layer(transaction layer) processing.

The host-side data transfer control device 10 includes an internalregister 250. The internal register 250 includes a port access register,a configuration register, an LVDS register, an interrupt controlregister, a target (RX) register, a power-down mode setting register,and the like. The system device writes an address (command) or data(parameter) into the internal register 250 through the system bus, orreads read data, status information, or the like from the internalregister 250. The information in the target register of the internalregister 250 is packetized and transferred to an internal register 350of the target-side data transfer control device 30 through the serialbus. Specifically, the target-side internal register 350 is a subset(shadow register) of the host-side internal register 250.

The host-side data transfer control device 10 (link controller 100)includes a power-down setting circuit 260 which performs power-downsettings. The power-down setting circuit 260 perform s power-downsetting processing of a PLL circuit 12, transmitter circuits 22 and 24,and receiver circuits 26 and 28 included in the transceiver 20. In moredetail, the power-down setting circuit 260 performs power-down controlbased on power-down information set in the power-down setting registerof the internal register 250. The system device such as the CPU sets thepower-down information in the internal register 250 through theinterface circuit 210. A power-down setting terminal may be provided tothe host-side data transfer control device 10, and the power-downinformation may be set through the terminal. The transmitter circuit maybe powered down by setting a power-down signal PDIN at active or settinginput signals DIN+/− at inactive as described later, for example. Thereceiver circuit may be powered down by cutting a current path of acurrent source included in the receiver circuit as described later, forexample.

The target-side data transfer control device 30 includes a transceiver40 (serial interface circuit) which performs physical layer processingor the like. The transceiver 40 receives a packet from the host-sidedata transfer control device 10 through the serial bus. The transceiver40 transmits a packet to the host-side data transfer control device 10.In this case, the link controller 300 generates a packet to betransmitted, and directs transmission of the generated packet.

The target-side data transfer control device 30 includes the linkcontroller 300. The link controller 300 performs link layer (transactionlayer) processing of receiving a packet from the host-side data transfercontrol device 10 and analyzing the received packet.

The target-side data transfer control device 30 includes an interfacecircuit 310 which performs interface processing between the datatransfer control device 30 and one or more devices (liquid crystaldisplay device, camera, and the like) connected with the interface bus.The interface circuit 310 may include an RGB interface circuit, an MPUinterface circuit, a serial interface circuit, and the like (not shown).

The target-side data transfer control device 30 includes the internalregister 350. The internal register 350 stores information necessary forthe target. In more detail, the internal register 350 stores interfaceinformation for specifying the signal form (output format) of aninterface signal output from the interface circuit 310 or the like.

2. Serial Transfer Method

A serial transfer method in this embodiment and a configuration exampleof the transceivers 20 and 40 are described below. In this embodiment,the host-side data transfer control device 10 is the side which suppliesa clock signal, and the target-side data transfer control device 30 isthe side which operates using the supplied clock signal as a systemclock signal.

In FIG. 1, DTO+ and DTO− are data (OUT data) output to the target (datatransfer control device 30) from the host (data transfer control device10). CLK+ and CLK− are clock signals supplied to the target from thehost. The host outputs the data DTO+/− in synchronization with the edge(rising edge, for example, but may be falling edge) of the clock signalsCLK+/−. Therefore, the target can sample and capture the data DTO+/−using the clock signals CLK+/−. In FIG. 1, the target operates based onthe clock signals CLK+/− supplied from the host. Specifically, the clocksignals CLK+/− become the system clock signals of the target. Therefore,the phase locked loop (PLL) circuit 12 (clock generation circuit in abroad sense) is provided in the host, and is not provided in the target.

DTI+ and DTI− are data (IN data) output to the host from the target.STB+ and STB− are strobes (clock signals in a broad sense) supplied tothe host from the target. The target generates and outputs the strobesSTB+/− based on the clock signals CLK+/− supplied from the host. Thetarget outputs the data DTI+/− in synchronization with the edge (risingedge, for example, but may be falling edge) of the strobes STB+/−.Therefore, the host can sample and capture the data DTI+/− using thestrobes STB+/−.

Each of the data DTO+/−, the clock signals CLK+/−, the data DTI+/−, andthe strobes STB+/− is transmitted by allowing a transmitter circuit(driver circuit) to current-drive the corresponding differential signallines (serial signal line in a broad sense). In order to realize ahigher speed transfer, two or more pairs of the DTO+/− differentialsignal lines and the DTI+/− differential signal lines may be provided.

The host-side transceiver 20 includes OUT-transfer (data transfer in abroad sense) and clock-transfer transmitter circuits 22 and 24, andIN-transfer (data transfer in a broad sense) and strobe-transfer (clocktransfer in a broad sense) receiver circuits 26 and 28. The target-sidetransceiver 40 includes OUT-transfer and clock-transfer receivercircuits 42 and 44, and IN-transfer and strobe-transfer transmittercircuits 46 and 48. A configuration in which some of these circuitblocks are omitted may be employed. In the case where a full-duplextransfer is unnecessary, a configuration in which the host-side receivercircuits 26 and 28 and the target-side transmitter circuits 46 and 48are omitted may be employed.

The OUT-transfer and clock-transfer transmitter circuits 22 and 24respectively transmit the data DTO+/− and the clock signals CLK+/− bycurrent-driving the DTO+/− differential signal lines and the CLK+/−differential signal lines (driving the serial signal lines in a broadsense). The OUT-transfer and clock-transfer receiver circuits 42 and 44respectively receive the data DTO+/− and the clock signals CLK+/− byperforming a current/voltage conversion based on the current which flowsthrough the DTO+/− differential signal lines and the CLK+/− differentialsignal lines, and performing comparison processing (differentialamplification processing) between differential voltage signals (firstand second voltage signals) obtained by the current/voltage conversion.

The IN-transfer and clock-transfer transmitter circuits 46 and 48respectively transmit the data DTI+/− and the strobes STB+/− bycurrent-driving the DTI+/− differential signal lines and the STB+/−differential signal lines (driving the serial signal lines in a broadsense). The IN-transfer and strobe-transfer receiver circuits 26 and 28respectively receive the data DTI+/− and the strobes STB+/− byperforming a current/voltage conversion based on the current which flowsthrough the DTI+/− differential signal lines and the STB+/− differentialsignal lines, and performing comparison processing (differentialamplification processing) between differential voltage signals (firstand second voltage signals) obtained by the current/voltage conversion.The following description is given taking a differential transfer methodusing the differential signals as an example. However, this embodimentmay also be applied to a single end transfer.

3. Normal Operation

A normal operation of the data transfer control device is describedbelow using FIG. 2A. As shown in FIG. 2A, the host-side transmittercircuits 22 and 24 and receiver circuits 26 and 28 are appropriatelydenoted by OUTTX, CLKTX, INRX, and STBRX, respectively. The target-sidetransmitter circuits 42 and 44 and receiver circuits 46 and 48 areappropriately denoted by OUTRX, CLKRX, INTX, and STBTX, respectively.

In the normal operation, OUTTX, CLKTX, INRX, STBRX, OUTRX, CLKRX, INTX,and STBTX are set to a normal operation mode. A host-side logic circuit220 (link controller 200, interface circuit 210, and a part of thecircuits of the transceiver 20) outputs parallel data to aparallel/serial conversion circuit 230. The serial/parallel conversioncircuit 230 converts the parallel data into serial data and outputs theserial data to OUTTX. The PLL circuit 12 generates a clock signal CLKand outputs the clock signal CLK to CLKTX and a frequency dividercircuit 234. The frequency divider circuit 234 generates a host-sidesystem clock signal HSYSCLK by dividing the frequency of the clocksignal CLK from the PLL circuit 12, and outputs the system clock signalHSYSCLK to the logic circuit 220. The host-side logic circuit 220operates based on the system clock signal HSYSCLK.

The host-side OUTTX and CLKTX respectively transmit OUT data and a clocksignal to the target-side OUTRX and CLKRX by current-driving the DTO+/−and CLK+/− serial signal lines. The target-side OUTRX and CLKRX receivethe OUT data and the clock signal. A target-side serial/parallelconversion circuit 330 samples the serial OUT data received by the OUTRXbased on the clock signal CLK received by CLKRX. The serial/parallelconversion circuit 330 converts the sampled serial data into paralleldata and outputs the parallel data to a logic circuit 320 (linkcontroller 300, interface circuit 310, and a part of the circuits of thetransceiver 40). A frequency divider circuit 334 generates a target-sidesystem clock signal TSYSCLK by dividing the frequency of the clocksignal CLK received by CLKRX, and outputs the system clock signalTSYSCLK to the logic circuit 320. The target-side logic circuit 320operates based on the system clock signal TSYSCLK.

The target-side logic circuit 320 outputs parallel data to theparallel/serial conversion circuit 340. The serial/parallel conversioncircuit 340 converts the parallel data into serial data and outputs theserial data to INTX. A strobe control circuit (frequency dividercircuit) 342 performs strobe control of the clock signal CLK received byCLKRX, and outputs a strobe STB to STBTX. In more detail, the strobecontrol circuit 342 generates the strobe STB by dividing the frequencyof the clock signal CLK at an arbitrary dividing ratio. As the strobecontrol, clock phase control and clock delay control and the like can begiven in addition to the frequency dividing control.

The target-side INTX and STBTX respectively transmit the IN data and thestrobe to the host-side INRX and STBRX by current-driving the DTI+/− andSTB+/− serial signal lines. The host-side INRX and STBRX receive the INdata and the strobe. The host-side serial/parallel conversion circuit240 samples the serial IN data received by INRX based on the strobe STBreceived by STBRX. The serial/parallel conversion circuit 240 convertsthe sampled serial data into parallel data and outputs the parallel datato the logic circuit 220.

In a conventional data transfer control method such as a digital visualinterface (DVI) (Japanese Patent Application Laid-open No. 2003-218843),PLL circuits are provided to transmission-side and reception-side datatransfer control devices. Since the amount of power consumption of thePLL circuit accounts for a considerable portion of power consumption ofthe data transfer control device, it is difficult to realize a reductionof power consumption of the data transfer control device by using theconventional method.

Moreover, the phase of the clock signal generated by thetransmission-side PLL circuit differs from the phase of the clock signalgenerated by the reception-side PLL circuit. Moreover, it is difficultto allow the frequencies of these clock signals to accurately coincidedue to the difference in vibration frequency (frequency of crystaloscillator). Therefore, the conventional method requires a complicatedcircuit for preventing sampling errors, FIFO overflow/underflow, and thelike. This poses a problem such as an increase in the scale of the datatransfer control device or an increase in power consumption.

In this embodiment, the host transmits the clock signal CLK to thetarget, and the target generates the system clock signal TSYSCLK basedon the received clock signal CLK, as shown in FIG. 2A. The targetgenerates the strobe STB based on the received clock signal, and outputsthe strobe STB to the host as the strobe STB for sampling the IN data.Therefore, by providing the PLL circuit 12 (clock generation circuit)only in the host, it may be unnecessary to provide a PLL circuit in thetarget. Therefore, power consumption of the target-side data transfercontrol device 30 can be significantly reduced in comparison with theconventional method.

Since the target-side system clock signal SYSCLK is generated based onthe clock signal CLK transmitted from the host, the target can be set tothe power-down mode merely by stopping the supply of the clock signalCLK from the host. Therefore, power-down control can be simplified asdescribed later.

Moreover, since the target can sample the OUT data based on the clocksignal CLK received from the host, it is unnecessary to provide acomplicated circuit for preventing sampling errors, FIFOoverflow/underflow, and the like. Therefore, a reduction of scale andpower consumption of the data transfer control device can be achieved.

In this embodiment, a full-duplex transfer in which data is receivedwhile transmitting data can be realized by providing INRX, STBRX, INTX,and STBTX as shown in FIG. 2A. In present embodiment, the targetgenerates the strobe STB based on the clock signal CLK transmitted fromthe host, and the host can sample the IN data using the strobe STBgenerated in this manner. Therefore, a problem in which the phase of theclock signal CLK and the phase of the strobe STB gradually shift fromeach other with the progress of time does not occur. As a result,occurrence of sampling errors or FIFO overflow/underflow can beprevented.

Specifically, in the conventional method in which the PLL circuits areprovided to the transmission side and the reception side, the vibrationfrequency (frequency of crystal oscillator) of the transmission-side PLLcircuit is not accurately the same as the vibration frequency of thereception-side PLL circuit. Therefore, since the phase of thetransmission-side clock signal CLK and the phase of the reception-sidestrobe STB gradually shift from each other with the progress of time, aphase adjustment circuit with a complicated configuration is necessary.

In this embodiment, since the strobe STB is generated based on the clocksignal CLK, the vibration frequencies of the strobe STB and the clocksignal CLK are the same. Therefore, a phenomenon in which the phase ofthe strobe STB and the phase of the clock signal CLK gradually shiftfrom each other with the progress of time does not occur. Therefore,after the circuit (delay value) is formed so that the IN data can besecurely sampled by using the strobe STB, the IN data can be securelysampled by using the strobe STB without providing a phase adjustmentcircuit with a complicated configuration. Moreover, occurrence ofoverflow/underflow of the FIFO which stores the IN data can beeffectively prevented.

4. Power-Down Mode

The power-down mode in this embodiment is described below. In thisembodiment, power-down modes M1, M2, M3, and M4 are provided as shown inFIG. 4. The power-down modes M1 to M4 are set when the system devicewrites the power-down information into the host-side internal register250.

As shown in FIG. 2B, in the first power-down mode M1, the power-downsetting circuit 260 sets OUTTX and CLKTX to the power-down mode. Thesystem clock signal TSYSCLK of the target-side data transfer controldevice 30 is stopped by setting CLKTX to the power-down mode, and thetarget automatically transitions to the power-down mode.

As shown in FIG. 3A, in the second power-down mode M2, the power-downsetting circuit 260 sets OUTTX to the power-down mode without settingCLKTX to the power-down mode.

In the case of a configuration which can realize a full-duplex datatransfer, the power-down setting circuit 260 sets OUTTX, CLKTX, NRX, andSTBRX to the power-down mode. In the power-down mode M2, the power-downsetting circuit 260 sets OUTTX, INRX, and STBRX to the power-down modewithout setting CLKTX to the power-down mode.

In the third power-down mode M3 in this embodiment, the power-downsetting circuit 260 sets the reception-side INRX and STBRX to thepower-down mode without setting the transmission-side OUTTX and CLKTX tothe power-down mode, as shown in FIG. 3B. In the fourth power-down modeM4, OUTTX, INRX, and STBRX automatically transition to the power-downmode as shown in FIG. 4. When the OUT-transfer stops for a predeterminedperiod and the host enters the idle state or the like, OUTTX isautomatically set to the power-down mode. When the IN transfer stops fora predetermined period and the host enters the idle state or the like,INRX and STBRX are automatically set to the power-down mode.

In the power-down mode M1 in this embodiment, the target-side OUTRX,CLKRX, INTX, and STBTX are set to the power-down mode as shown in FIG.2B. In the power-down mode M2, the target-side OUTRX, INTX, and STBTXare set to the power-down mode as shown in FIG. 3A. In the power-downmode M3, the target-side INTX, and STBTX are set to the power-down modeas shown in FIG. 3B. This may be realized by allowing the host-sidetransmitter circuit to transmit a power-down command for setting thereceiver circuit to the power-down mode to the receiver circuitconnected with the transmitter circuit by current-driving the serialsignal lines using a current driver, as described later. In this case,it is preferable to transmit the power-down command by current-drivingthe data transfer serial signal lines instead of the clock-transferserial signal lines, as described later.

For example, in the conventional method in which the PLL circuits areprovided to the transmission side and the reception side, apredetermined procedure of stopping the reception-side PLL circuit isnecessary for setting the reception side to the power-down mode, wherebypower-down control becomes complicated.

According to this embodiment, the target-side system clock signalTSYSCLK is automatically stopped by setting CLKTX to the power-down modeby the power-down mode M1. This enables the target to be automaticallyset to the power-down mode, whereby the power-down control can besimplified.

According to this embodiment, the power-down mode M2 is provided inaddition to the power-down mode M1. In the power-down mode M2, OUTTX andthe like are set to the power-down mode. However, since CLKTX is not setto the power-down mode, the target-side system clock signal TSYSCLK isnot stopped. Therefore, even if the data transfer control devices areset to the power-down mode M2, the target-side logic circuit 320 whichoperates based on the system clock signal TSYSCLK can take actionagainst the host. In particular, in the case of a configuration whichrealizes a full-duplex data transfer, the power-down mode of INTX andSTBTX can be canceled by allowing the target to take action against thehost, whereby the IN data transfer can be resumed.

In the power-down mode M2, CLKTX is not set to the power-down mode, andOUTTX, INRX, and STBRX are set to the power-down mode. Therefore, sinceOUTTX, INRX, and STBRX, which consume a considerable amount of power inthe data transfer control device, can be set to the power-down mode,power consumption can be reduced.

In this embodiment, only INRX and STBRX can be set to the power-downmode by setting the data transfer control device to the power-down modeM3. Therefore, when only the data transfer from the host to the targetis performed and the data transfer from the target to the host is notperformed (when full-duplex transfer is not performed), INRX and STBRXwhich need not operate can be set to the power-down mode, whereby powerconsumption can be reduced. Therefore, a more minute and intelligentpower-down control can be realized.

5. Strobe Control Circuit

FIG. 5 shows a configuration example of the strobe control circuit 342.The strobe control circuit 342 includes a frequency divider circuit 343and selectors 344 and 345.

The frequency divider circuit 343 may be formed by a plurality of stagesof serially-connected D flip-flop circuits. A plurality of outputsignals from four stages of D-flip-flop circuits are input to theselector 344.

A signal TxSpeed is a signal for determining the dividing ratio of thestrobe STB with respect to the clock signal CLK. The selector 344selects one of the output signals of a plurality of stages ofD-flip-flop circuits of the frequency divider circuit 343 based on thesignal TxSpeed, and outputs the selected signal to a data terminal ofthe D-flip-flop circuit in the first stage of the frequency dividercircuit 344, for example. This enables the frequency divider circuit 343to generate a signal DSTB obtained by dividing the frequency of theclock signal CLK.

The signal DSTB from the frequency divider circuit 343 is input to afirst input of the selector 345, and the clock signal CLK is input to asecond input of the selector 345. The selector 345 selects the signalDSTB or the clock signal CLK based on the signal TxSpeed, and outputsthe selected signal as the strobe STB. For example, the selector 345selects the clock signal CLK when the signal TxSpeed indicates adividing ratio of “1”, and selects the signal DSTB when the signalTxSpeed indicates another dividing ratio.

A signal Enable is a signal which controls enabling/disabling of outputof the strobe STB. A signal INIT is a control signal for initializingthe frequency divider circuit 343. A signal XRST is a reset signal.

The data transfer rate of the IN transfer can be arbitrarily changed byproviding the strobe control circuit 342 shown in FIG. 5, whereby aflexible data transfer control corresponding to the transfer data can berealized. The strobe control circuit 342 is not limited to theconfiguration shown in FIG. 5. A configuration which performs not onlythe frequency dividing control, but also strobe control such as phasecontrol (delay control) may be employed, for example.

6. Asynchronous Transfer

In FIG. 6, in this embodiment, the IN data is transferred from thetarget in synchronization with the strobe STB. The host-side logiccircuit 220 which receives the IN data operates in synchronization withthe clock signal CLK generated by the PLL circuit 12. In more detail,the logic circuit 220 operates based on the system clock signal HSYSCLKgenerated by allowing the frequency divider circuit 234 to divide thefrequency of the clock signal CLK. Therefore, the target must deliverdata by asynchronous transfer.

In this embodiment, the serial/parallel conversion circuit 240asynchronously transfers parallel data to the logic circuit 220 in thesubsequent stage, as shown in FIG. 6.

In this embodiment, the transfer rate through the serial signal line ishigh (200 Mbps, for example). Therefore, since a critical path occurswhen asynchronous transfer is performed through a path at such a hightransfer rate, a stable asynchronous transfer cannot be realized. Thetransfer rate of the parallel data converted by the serial/parallelconversion circuit 240 is sufficiently lower than the transfer rate ofthe serial data. In the case where the serial data is converted into16-bit parallel data, the transfer rate is reduced by 1/16, for example.

In FIG. 6, asynchronous transfer is performed in the path between theserial/parallel conversion circuit 240 and the logic circuit 220, whichis the path in which the transfer rate is low. Therefore, the criticalpath or the like rarely occurs, whereby a stable asynchronous transfercan be realized. As the circuit in the subsequent stage of theserial/parallel conversion circuit 240, a circuit which decodes an8B/10B code or the like can be given.

7. Configuration of Transmitter Circuit and Receiver Circuit FIG. 7shows a configuration example of the transmitter circuit (drivercircuit) and the receiver circuit in this embodiment. The configurationsand operations of the transmitter circuit and the receiver circuit forthe data DTO+/− are mainly described below. However, the configurationsand operations of the transmitter circuits and the receiver circuits forthe clock signals CLK+/−, the data DTI+/−, and the strobes STB+/− arethe same as those of the transmitter circuit and the receiver circuitfor the data DTO+/−.

A transmitter circuit 50 includes a current driver 60 and a voltagedriver 70. A receiver circuit 80 includes a current/voltage conversioncircuit 90, a comparator 100, a power-down detection circuit 110, apower-down setting circuit 120, and a wakeup detection circuit 130(wakeup detection buffer). The power-down setting circuit 120 may have aconfiguration in which some of these circuit blocks are omitted.

The current driver 60 is a driver which current-drives the DTO+/−differential signal lines (serial signal lines in a broad sense). Inmore detail, the current driver 60 alternately repeats a current drivewhich causes current to flow through the DTO+ signal line (first signalline of the differential signal lines in a broad sense) and a currentdrive which causes current to flow through the DTO− signal line (secondsignal line of the differential signal lines in a broad sense). Thecurrent driver 60 may alternately repeat a current drive in a firstcurrent path consisting of the DTO+ signal line as the outward path andthe DTO− signal line as the return path (current path from the DTO+signal line to the DTO− signal line) and a current drive in a secondcurrent path consisting of the DTO− signal line as the outward path andthe DTO+ signal line as the return path (current path from the DTO−signal line to the DTO+ signal line). The current driver 60 may beformed by a current source (constant current source), a switching device(transistor) which performs current control for causing current from thecurrent source to flow through the DTO+/− signal lines, and the like.

The voltage driver 70 is electrically disconnected from the DTO+/−differential signal lines (serial signal lines) in a normal transfermode, and is connected with the differential signal lines andvoltage-drives the differential signal lines in a power-down mode. Thevoltage driver 70 outputs a power-down voltage (voltage for setting thereceiver circuit 80 to the power-down mode) or a wakeup voltage (voltagefor canceling the power-down mode of the receiver circuit 80) to thedifferential signal lines. The voltage driver 70 may be formed by acircuit which outputs the power-down voltage or the wakeup voltage at aCMOS voltage level (voltage level which can cause a CMOS transistor tobe turned ON/OFF), a switching device (transistor) which electricallyconnects/disconnects the output of the circuit with/from thedifferential signal lines, and the like.

The normal transfer mode is a mode in which the data or the clock signal(strobe) is normally transferred between the host and the target. Thepower-down mode is a mode in which power consumption is reduced bylimiting or stopping current which flows through the transmittercircuit, the receiver circuit, or other circuits included in the device.In the voltage drive, the voltage of the differential signal lines ischanged at the CMOS voltage level, for example. In the current drive,the voltage of the differential signal lines is changed at a voltagelower than the CMOS voltage level.

The current/voltage conversion circuit 90 performs a current/voltageconversion based on the current which flows through the differentialsignal lines, and outputs first and second voltage signals VS1 and VS2which make up the differential voltage signals. In more detail, when thetransmitter circuit 50 current-drives the DTO+ signal line, thecurrent/voltage conversion circuit 90 performs a current/voltageconversion based on the current which flows through the DTO+ signal lineto generate the first voltage signal VS1. When the transmitter circuit50 current-drives the DTO− signal line, the current/voltage conversioncircuit 90 performs a current/voltage conversion based on the currentwhich flows through the DTO− signal line to generate the second voltagesignal VS2. Or, when the transmitter circuit 50 alternately repeats thecurrent drive in the first current path from the DTO+ signal line to theDTO− signal line and the current drive in the second current path fromthe DTO− signal line to the DTO+ signal line, the current/voltageconversion circuit 90 may generate the first and second voltage signalsVS1 and VS2 across a resistor element (termination resistor) providedbetween the input node of the DTO+ signal line and the input node of theDTO− signal line.

The comparator (operational amplifier) 100 compares the first and secondvoltage signals VS1 and VS2 (amplifies the voltage between the first andsecond voltage signals VS1 and VS2), and outputs an output signal CQ(amplified signal). The comparator 100 outputs the output signal CQ atthe H level (logic “1”) of the CMOS voltage level when the voltage ofthe first voltage signal VS1 is higher than the voltage of the secondvoltage signal VS2, for example. The comparator 100 outputs the outputsignal CQ at the L level (logic “0”) of the CMOS voltage level when thevoltage of the second voltage signal VS2 is higher than the voltage ofthe first voltage signal VS1, for example.

The power-down detection circuit 110 is a circuit which detects apower-down command. In more detail, when the transmitter circuit 50transmits the power-down command by current-driving the differentialsignal lines in the normal transfer mode (when the transmitter circuit50 transmits transfer data including the power-down command), thepower-down detection circuit 110 detects the transmitted power-downcommand based on the detection result from the comparator 100. In thiscase, the power-down detection circuit 110 may convert the output signalCQ from the comparator 100 from serial data to parallel data, and detectthe power-down command based on the converted parallel data (detectionresult in a broad sense). The power-down detection circuit 110 maydirectly detect the power-down command from the output signal CQ(detection result in a broad sense) in the form of serial data.

The power-down setting circuit 120 is a circuit which sets the receivercircuit 80 to the power-down mode. In more detail, the power-downsetting circuit 120 sets the current/voltage conversion circuit 90 andthe comparator 100 to the power-down mode when the power-down command isdetected. In this case, the power-down setting circuit 120 may set onlyone of the current/voltage conversion circuit 90 and the comparator 100to the power-down mode, or may set both the current/voltage conversioncircuit 90 and the comparator 100 to the power-down mode. Or, othercircuits included in the receiver circuit 80 may be set to thepower-down mode, or other circuits included in the target-side datatransfer control device which includes the receiver circuit 80 orincluded in the host-side data transfer control device may be set to thepower-down mode.

The wakeup detection circuit 130 is a circuit for detecting the wakeupstate. In more detail, the wakeup detection circuit 130 detects thewakeup voltage output to the differential signal lines (at least one ofthe DTO+ signal line and the DTO− signal line) from the voltage driver70. When the wakeup detection circuit 130 detects the wakeup voltage,the power-down mode set by the power-down setting circuit 120 iscanceled, whereby the receiver circuit 80 transitions to the normaltransfer mode. The wakeup detection circuit 130 may be a circuit whichoutputs the wakeup signal when cancellation of the power-down mode isdetected after the receiver circuit 80 has been set to the power-downmode by output of the power-down voltage to the differential signallines.

In this embodiment, the transmitter circuit 50 transmits the power-downcommand to the receiver circuit 80 by current-driving the differentialsignal lines. When the power-down detection circuit 110 detects thetransmitted power-down command, the power-down setting circuit 120 setsthe current/voltage conversion circuit 90 and the comparator 100 to thepower-down mode. Therefore, according to this embodiment, current whichconstantly flows through the current/voltage conversion circuit 90 andthe comparator 100 can be limited or stopped in the power-down mode,whereby power consumption can be reduced.

Moreover, according to this embodiment, the transmitter circuit 50 canindividually set the receiver circuit 80 to the power-down mode.Specifically, in FIG. 1, the OUT-transfer and clock-transfer transmittercircuits 22 and 24 can respectively and individually set theOUT-transfer and clock-transfer receiver circuits 42 and 44 to thepower-down mode. Or, the IN-transfer and strobe-transfer transmittercircuits 46 and 48 can respectively and individually set the IN-transferand strobe-transfer receiver circuits 26 and 28 to the power-down mode.Therefore, a more minute and intelligent power-down control can berealized.

According to this embodiment, since the power-down command istransmitted in the normal transfer mode through the differential signallines (serial signal lines), it is unnecessary to separately provide acontrol signal line exclusively for transmission of the power-downcommand. Therefore, since the number of signal lines can be reduced, areduction of the circuit scale, facilitation of mounting, and areduction of product cost can be achieved.

According to this embodiment, the voltage driver 70 is electricallyconnected with the differential signal lines in the power-down mode, andoutputs the wakeup voltage to the receiver circuit 80 through thedifferential signal lines. When the wakeup detection circuit 130 detectsthe wakeup voltage, the power-down mode is canceled. Therefore, thetransmitter circuit 50 can cancel the power-down mode of the receivercircuit 80, even if the current/voltage conversion circuit 90 and thecomparator 100 are set to the power-down mode and a power-down cancelcommand cannot be transmitted by current-driving the differential signallines. Moreover, since the power-down mode is canceled byvoltage-driving the differential signal lines using the wakeup voltage,it is unnecessary to separately provide a control signal lineexclusively for transmission of the power-down cancel command. As aresult, since the number of signal lines can be reduced, a reduction ofthe circuit scale, facilitation of mounting, and a reduction of productcost can be achieved.

According to this embodiment, when the power-down voltage is output tothe differential signal lines by the voltage driver 70 after thepower-down command has been transmitted, the receiver circuit 80 is setto the power-down mode. When cancellation of the power-down mode isdetected, the wakeup detection circuit 130 outputs the wakeup signal.This facilitates the power-down setting and the cancellation sequence.

According to this embodiment, the voltage driver 70 is electricallydisconnected from the differential signal lines in the normal transfermode. Therefore, an adverse effect on the normal transfer, in which thedifferential signal lines are current-driven, can be minimized.

8. First Configuration Example

FIG. 8 shows a detailed first configuration example of the transmittercircuit and the receiver circuit. The transmitter circuit and thereceiver circuit do not necessarily include all of the circuit elementsshown in FIG. 8. The transmitter circuit and the receiver circuit mayhave a configuration in which some of the circuit elements are omitted.

The current driver 60 of the transmitter circuit includes an N-type(first conductivity type in a broad sense) transistor TR1A (firstcurrent source in a broad sense) provided between a first output nodeNQA and a power supply VSS (first power supply in a broad sense) on theside of the DTO+ signal line (first signal line in a broad sense). Thecurrent driver 60 includes an N-type transistor TR1B (second currentsource in a broad sense) provided between a second output node NQB andthe power supply VSS on the side of the DTO− signal line (second signalline in a broad sense). In more detail, the output node NQA is connectedwith a drain terminal of the transistor TR1A, a positive-side firstinput signal DIN+is input to a gate terminal of the transistor TR1A, andthe power supply VSS is connected with a source terminal of thetransistor TR1A. The output node NQB is connected with a drain terminalof the transistor TR1B, a negative-side second input signal DIN− isinput to a gate terminal of the transistor TR1B, and the power supplyVSS is connected with a source terminal of the transistor TR1B. Acertain amount of current is caused to flow through the current sourcesformed by the transistors TR1A and TR1B, for example.

The transistor TR1A is turned ON when the input signal DIN+becomesactive (H level), whereby current flows through the path from the inputnode NIA of the receiver circuit on the side of the DTO+ signal line tothe output node NQA of the transmitter circuit. The transistor TR1B isturned ON when the input signal DIN− becomes active, whereby currentflows through the path from the input node NIB of the receiver circuiton the side of the DTO− signal line to the output node NQB of thetransmitter circuit. Therefore, the DTO+/− differential signal lines canbe differentially current-driven by alternately activating the inputsignals DIN+ and DIN−.

In FIG. 8, the transistors TR1A and TR1B have the function of thecurrent source and the function of controlling the current which flowsthrough the current source. However, the current source provided betweenthe node NQA and the power supply VSS (first power supply) may be formedby the transistor TR1A (switching device in a broad sense) and a currentsource (transistor to which a reference voltage is input at a gateterminal, for example) provided between the transistor TR1A and thepower supply VSS. The current source provided between the node NQB andthe power supply VSS may be formed by the transistor TR1B (switchingdevice in a broad sense) and a current source provided between thetransistor TR1B and the power supply VSS. This realizes control whichcauses or does not cause the current from the current sources (constantcurrent sources) to flow through the DTO+/− differential signal lines byON/OFF controlling the transistors TR1A and TR1B. The current sourceprovided between the node NQA and the power supply VSS may be formed bya current source (constant current source) which causes a large amountof current (constant current) to flow when the input signal DIN+ isactive (H level), and causes a small amount of current (constantcurrent) to flow when the input signal DIN+ is inactive (L level). Thecurrent source provided between the node NQB and the power supply VSSmay be formed by a current source (constant current source) which causesa large amount of current (constant current) to flow when the inputsignal DIN− is active, and causes a small amount of current (constantcurrent) to flow when the input signal DIN− is inactive. In FIG. 8, thecurrent sources realized by the transistors TR1A and TR1B respectivelycause current to flow from the receiver circuit to the transmittercircuit when the input signals DIN+ and DIN− are active. However, thecurrent sources may cause current to flow from the transmitter circuitto the receiver circuit. In this case, the first power supply is a powersupply VDD, for example.

The voltage driver 70 of the transmitter circuit includes an N-typetransistor TR2A (switching device in a broad sense). The transistor TR2Afunctions as a switching device which is turned OFF in the normaltransfer mode and is turned ON in the power-down mode. The output nodeNQA (or NQB) is connected with a source terminal of the transistor TR2A,and the output of the voltage output circuit 72 is connected with adrain terminal of the transistor TR2A. The transistor TR2A is turned OFFin the normal transfer mode and is turned ON in the power-down modebased on a power-down input signal PDIN input to the gate terminal. Thisallows the voltage driver 70 to be electrically disconnected from thedifferential signal lines in the normal transfer mode and to beelectrically connected with the differential signal lines in thepower-down mode. The voltage driver 70 voltage-drives the differentialsignal lines by using the voltage output circuit 72 when connected withthe differential signal lines.

A wakeup input signal XWUPIN and the power-down input signal PDIN aregenerated by a layer (link layer or application layer) higher than thetransmitter circuit which is a physical layer circuit. Specifically,when setting the receiver circuit to the power-down mode, the higherlayer (power-down setting circuit) sets the signal PDIN at active (Hlevel). When canceling the power-down mode of the receiver circuit, thehigher layer (power-down setting circuit) sets the signal XWUPIN atactive (L level).

The voltage output circuit 72 (voltage output buffer) is a circuit whichvoltage-drives the differential signal lines by outputting the signalXWUP at the CMOS voltage level. The voltage output circuit 72 outputs avoltage at the H level of the CMOS voltage level in the power-down mode(initial stage of the power-down mode), for example. The voltage outputcircuit 72 outputs a voltage (wakeup voltage) at the L level of the CMOSvoltage level when canceling the power-down mode, for example.

In FIG. 8, the voltage output circuit 72 and the transistor TR2A whichmake up the voltage driver 70 are provided on the side of the DTO+signal line (between the power supply VDD and the output node NQA).However, the voltage output circuit 72 and the transistor TR2A may beprovided on the side of the DTO− signal line (between the power supplyVDD and the output node NQB). A part or the entirety of the voltagedriver 70 may be provided both on the side of the DTO+ signal line andthe side of the DTO− signal line.

The current/voltage conversion circuit 90 of the receiver circuitincludes a transistor TR3A (first current source on the side of thereceiver circuit in a broad sense) provided between the input node NIAand the power supply VSS (first power supply), and a transistor TR3B(second current source on the side of the receiver circuit in a broadsense) provided between the input node NIB and the power supply VSS. Acertain amount of current is caused to flow through the current sourcesformed by the transistors TR3A and TR3B. The voltages of the input nodesNIA and NIB and the voltage output nodes NVA and NVB can be maintainedwithin a predetermined range by causing current to constantly andcontinuously flow through the transistors TR3A and TR3B, even if thetransistors TR1A and TR1B are in the OFF state . Therefore, theoperation speed of the current/voltage conversion circuit 90 can beincreased.

In FIG. 8, the transistors TR3A and TR3B have the function of thecurrent source and the function of controlling the current which flowsthrough the current source. However, the current source provided betweenthe node NIA and the power supply VSS (first power supply) may be formedby the transistor TR3A (switching device in a broad sense) and a currentsource (transistor to which the reference voltage is input at a gateterminal, for example) provided between the transistor TR3A and thepower supply VSS. The current source provided between the node NIB andthe power supply VSS may be formed by the transistor TR3B (switchingdevice in a broad sense) and a current source provided between thetransistor TR3B and the power supply VSS.

The current/voltage conversion circuit 90 includes a first invertercircuit INV1A (voltage amplifier circuit) of which the input isconnected with the input node NIA, and a second inverter circuit INV1B(voltage amplifier circuit) of which the input is connected with theinput node NIB. The current/voltage conversion circuit 90 includes anN-type transistor TR4A (first variable resistor element in a broadsense) of which the source terminal is connected with the input nodeNIA, the gate terminal is connected with the output of the invertercircuit INV1A, and the drain terminal is connected with the voltageoutput node NVA. The current/voltage conversion circuit 90 includes anN-type transistor TR4B (second variable resistor element in a broadsense) of which the source terminal is connected with the input nodeNIB, the gate terminal is connected with the output of the invertercircuit INV1B, and the drain terminal is connected with the voltageoutput node NVB.

The transistors TR4A and TR4B function as variable resistor elements ofwhich the resistance is variably controlled based on the voltages(potentials) of the input nodes NIA and NIB, respectively. The invertercircuits INV1A and INV1B function as circuits which control theON-resistance of the transistors TR4A and TR4B by amplifying the changesin voltage of the input nodes NIA and NIB, respectively. In more detail,when the transistors TR1A and TR1B are turned ON and the voltages of theinput nodes NIA and NIB are changed to the L (low) level, the invertercircuits INV1A and INV1B amplify the changes in voltage. This causes theoutput voltages of the inverter circuits INV1A and INV1B to be changedto the H (high) level, whereby the ON-resistance of the transistors TR4Aand TR4B is decreased. This enables the change in current which iscaused to flow by the transistors TR1A and TR1B to be amplified(accelerated), whereby the voltages of the voltage output nodes NVA andNVB can be quickly changed to the L level. Specifically, a minute changein current at the nodes NIA and NIB (transistors TR1A and TR1B) can beamplified and transmitted to the nodes NVA and NVB (transistors TR5A andTR5B) by providing the transistors TR4A and TR4B and the invertercircuits INV1A and INV1B. The current/voltage conversion circuit 90 mayhave a configuration in which the transistors TR4A and TR4B and theinverter circuits INV1A and INV1B are omitted.

The current/voltage conversion circuit 90 includes a P-type (secondconductivity type in a broad sense) transistor TR5A (firstcurrent/voltage conversion element in a broad sense) provided betweenthe voltage output node NVA and the power supply VDD (second powersupply in a broad sense), and a P-type transistor TR5B (secondcurrent/voltage conversion element in a broad sense) provided betweenthe voltage output node NVB and the power supply VDD. In more detail,the transistors TR5A and TR5B are connected with the power supply VDD ata source terminal and are connected with the voltage output nodes NVAand NVB at a gate terminal and a drain terminal, respectively. Thetransistors TR5A and TR5B function as current/voltage conversionelements (load elements) which convert current which flows between thepower supply VDD and the voltage output nodes NVA and NVB into voltage.The current/voltage conversion elements need not be formed by thetransistors TR5A and TR5B (load transistors), but may be formed by othercircuit elements such as resistors.

The current/voltage conversion circuit 90 includes a resistor RAprovided between the DTO+ signal line and the input node NIA, and aresistor RB provided between the DTO− signal line and the input nodeNIB. The resistors RA and RB are resistors for impedance matching. Thecurrent/voltage conversion circuit 90 may have a configuration in whichthe resistors RA and RB are omitted.

The output signal from the comparator 100 is input to a level shifter102, and the voltage level is converted (from 2.8 V to 1.8 V, forexample). The inversion output signal from the level shifter 102 isinput to a serial/parallel conversion circuit 104. The inversion outputsignal (negative logic) from the comparator 100 may be input to thelevel shifter 102, and the output signal (positive logic) from the levelshifter 102 may be input to the serial/parallel conversion circuit 104.

The serial/parallel conversion circuit 104 converts the serial data fromthe comparator 100 into parallel data. The parallel data output from theserial/parallel conversion circuit 104 is stored in a FIFO, and outputto a higher layer circuit in the subsequent stage (layer higher than thephysical layer).

The power-down detection circuit 110 detects the power-down commandbased on the parallel data (parallel signal) from the serial/parallelconversion circuit 104. In more detail, the power-down detection circuit110 detects the power-down command included in the data transmitted fromthe transmitter circuit in the normal transfer mode. The power-downdetection circuit 110 may directly detect the power-down command fromthe output signal from the comparator 100.

The power-down detection circuit 110 includes a command decoder 112 anda power-down pulse generation circuit 114. The command decoder 112detects the power-down command by the decode processing. When thetransmitter circuit transmits a special code generated by using anencoding method (8B/10B encoding, for example) which expands the bitwidth as the power-down command, the power-down detection circuit 110detects the special code to which the power-down command is assigned bydecode processing of the command decoder 112. The power-down pulsegeneration circuit 114 generates a power-down pulse signal PDPLS whenthe power-down command is detected. The power-down pulse generationcircuit 114 also performs processing of adjusting the generation timingof the signal PDPLS.

The power-down setting circuit 120 includes a holding circuit 122, adelay circuit 124, and level shifters 126 and 128. The power-downsetting circuit 120 may have a configuration in which some of thesecircuit blocks are omitted.

The holding circuit 122 holds power-down setting information (power-downsetting flag) when the power-down command is detected until thepower-down mode is canceled. In more detail, the holding circuit 122 isset when the signal PDPLS becomes active (L level), whereby the logic“1” (power-down setting information) is held. The holding circuit 122may be realized by an RS flip-flop with a reset terminal and a setterminal or the like.

The output signal from the holding circuit 112 is input to the delaycircuit 124, and delay processing of the signal is performed. The outputsignal from the delay circuit 124 is input to the level shifter 126, andthe voltage level is converted (from 1.8 V to 2.8 V). A positive logicpower-down signal PD, which is the output signal from the level shifter126, is input to an enable terminal XEN (negative logic) of thecomparator 100 and an enable terminal EN (positive logic) of the wakeupdetection circuit 130. A negative logic power-down signal XPD, which isthe inversion output signal from the level shifter 126, is input to thegate terminals of the transistors TR3A and TR3B.

The wakeup detection circuit 130 (wakeup detection buffer) is a circuitwhich detects the wakeup voltage when the transmitter circuit outputsthe wakeup voltage to the differential signal lines. The wakeupdetection circuit 130 operates at the CMOS voltage level, and detectsthe wakeup voltage at the CMOS voltage level. In FIG. 8, the wakeupdetection circuit 130 is connected with the DTO+ signal line. However,the wakeup detection circuit 130 may be connected with the DTO− signalline, or may be connected with both the DTO+ and DTO− signal lines.

Since the signal PD is set at the L level in the normal transfer mode,the comparator 100 is set to the enabled state and the wakeup detectioncircuit 130 is set to the disabled state. Since the signal XPD is set atthe H level, the transistors TR3A and TR3B are turned ON. Since thesignal PD is set at the H level when the power-down command is detected,the comparator 100 is set to the disabled state and set to thepower-down mode (mode in which the operating current is stopped orlimited), and the wakeup detection circuit 130 is set to the enabledstate. Since the signal XPD is set at the L level, the transistors TR3Aand TR3B are turned OFF, whereby the current/voltage conversion circuit90 is set to the power-down mode.

When the voltage output circuit 72 outputs the wakeup voltage at the Llevel in the power-down mode, the wakeup detection circuit 128 set tothe enabled state detects the wakeup voltage, and outputs a signalXWUPPLS which is a signal for canceling the power-down mode. The holdingcircuit 122 is reset when the pulse signal XWUPPLS at the L level fromthe wakeup detection circuit 128 is input to a reset terminal of theholding circuit 122 through the level shifter 128. This causes thepower-down setting information (logic “1”) to be cleared, whereby thepower-down mode is canceled.

FIG. 9 shows a configuration of the transmitter circuit and the receivercircuit, in which the voltage driver 70, the power-down detectioncircuit 110, and the power-down setting circuit 120 are not provided, asa comparative example.

9. Operation

The operation in the first configuration example shown in FIG. 8 isdescribed below using waveform diagrams shown in FIGS. 10 and 11. Theoperation in the normal transfer mode is described below. As shown inFIG. 10, since the signal PDIN is set at the L level in the normaltransfer mode, the transistor TR2A is in the OFF state. Since thepower-down signal PD is set at the L level, the transistors TR3A andTR3B are in the ON state. The voltage driver 70 is electricallydisconnected from the differential signal lines when the transistor TR2Ais turned OFF. A normal operating current flows through thecurrent/voltage conversion circuit 90 when the transistors TR3A and TR3Bare turned ON, whereby the normal transfer can be realized.Specifically, the configuration shown in FIG. 8 becomes equivalent tothe configuration shown in FIG. 9.

In the normal transfer mode, the transmitter circuit and the receivercircuit operate as described below. When the transistors TR1A and TR1Bare in the OFF state, the input nodes NIA and NIB are set at a voltageof about 1 V, for example. When the transistor TR1A on the side of theDTO+ signal line is turned ON, current flows toward the power supply VSS(GND) through the differential signal lines. This causes the voltage ofthe input node NIA to be decreased to only a small extent. As a result,the voltage of the input node NIA is reversed by the inverter circuitINV1A and the output voltage of the inverter circuit INV1A is increased,whereby the ON-resistance of the transistor TR4A is decreased. Thisincreases the amount of current which flows through the transistor TR5A.Therefore, the voltage difference between the power supply VDD and thevoltage output node NVA (voltage between the drain and source of thetransistor TR5A) is increased, whereby the voltage of the voltage outputnode NVA is decreased. When the transistor TR1B on the side of the DTO−signal line is turned ON, the voltage of the voltage output node NVB isdecreased. Therefore, the data “0” or “1” is detected by allowing thecomparator 100 to compare and amplify the voltage difference between thevoltage output nodes NVA and NVB.

The operation during power-down command transmission is described below.At Al shown in FIG. 10, the transmitter circuit transmits the power-downcommand to the receiver circuit. In this embodiment, since thepower-down command is transmitted in the normal transfer mode in whichthe differential signal lines are current-driven, it is unnecessary toprovide an extra signal line.

As indicated by A2 in FIG. 10, the transmitter circuit may transmit aplurality of power-down commands by current-driving the differentialsignal lines. The power-down setting circuit 120 may set thecurrent/voltage conversion circuit 90 and the comparator 100 to thepower-down mode on condition that a plurality of power-down commands aredetected.

A problem in which the receiver circuit 80 is erroneously set to thepower-down mode can be prevented, even when a transfer error occurs, bytransmitting and detecting a plurality of power-down commands.Specifically, if the receiver circuit 80 is erroneously set to thepower-down mode, it is difficult for the receiver circuit 80 to recoverfrom the power-down mode. However, such a problem can be prevented bytransmitting and detecting a plurality of power-down commands.

The operation at the time of power-down setting is described below. Asindicated by A3 shown in FIG. 10, the transistor TR2A is turned ON whenthe signal PDIN is set at the H level, whereby the voltage driver 70 iselectrically connected with the differential signal lines. The voltagedriver 70 outputs a voltage at the H level of the CMOS voltage level tothe differential signal lines as indicated by A4, whereby the transistorTR4A is turned OFF. An unnecessary current can be prevented from flowingthrough the path from the transistor TR5A to the voltage output circuit72 through the transistor TR4A, the DTO+ signal line, and the transistorTR2A by causing the transistor TR4A to be turned OFF, whereby powerconsumption can be reduced.

When the transmitter circuit transmits the power-down command, apower-down pulse signal PDPLS becomes active (L level) after the periodTD1 has elapsed as indicated by A5 shown in FIG. 10. The period TD1 canbe adjusted by the power-down pulse generation circuit 114. The logic“1” is set in the holding circuit 122 when the signal PDPLS becomesactive. As indicated by A6, the power-down signal PD becomes activeafter the period TD2 has elapsed. The period TD2 can be adjusted by thedelay circuit 124.

When the signal PD becomes active, the transistors TR3A and TR3B areturned OFF, and the comparator 100 is set to the disabled state.Therefore, the operating current which constantly flows through thecurrent/voltage conversion circuit 90 and the comparator 100 can be cut,whereby power consumption can be reduced. Moreover, since the wakeupdetection circuit 130 is set to the enabled state, the wakeup voltageoutput to the differential signal lines can be detected.

The operation at the time of power-down cancellation is described belowusing FIG. 11. As indicated by B1 shown in FIG. 11, a voltage at the Hlevel of the CMOS voltage level is output to the DTO+ (or DTO−) signalline in the power-down mode. When canceling the power-down mode, thevoltage output circuit 72 outputs the wakeup voltage at the L level ofthe CMOS voltage level to the DTO+ signal line as indicated by B2. Thesignal PDIN is set at the L level after the period TD3 has elapsed,whereby the transistor TR2A is turned OFF and the voltage output circuit72 is electrically disconnected from the DTO+ signal line.

When the wakeup voltage is output, the wakeup detection circuit 130 setto the enabled state detects the wakeup voltage, and sets the signalXWUPPLS at the L level as indicated by B4. This causes the holdingcircuit 122 to be reset to the logic “0”, and the power-down signal PDis set at the L level after the period TD4 has elapsed, as indicated byB5. This causes the transistors TR3A and TR3B to be turned ON and thecomparator 100 to be set to the enabled state, whereby the power-downmode is canceled. The wakeup detection circuit 130 is set to thedisabled state. As indicated by B6, the differential signal lines areset to the idle state after an undefined period, whereby the normaltransfer can be enabled.

10. Transmission of Power-Down Command Using Special Code

In this embodiment, encoding circuits 11 and 31 may be respectivelyprovided in the host-side data transfer control device 10 and thetarget-side data transfer control device 30 (transmitter circuit), asshown in FIG. 12A. The encoding circuits 11 and 31 encode the data usingan encoding method which expands the bit width, for example. As theencoding method, an 8B/10B encoding method in which 8-bit data isconverted into 10-bit data can be given, for example. According to the8B/10B encoding method, even if the data continuously contains “0” or“1”, a change in bits of the signal is increased after encoding as shownin FIG. 12B, whereby occurrence of transfer errors due to noise or thelike can be reduced. According to the 8B/10B encoding method, since thebit width is expanded from 8 bits to 10 bits, a special code (similar tocontrol code) shown in FIG. 12C can be transmitted in addition to data.

In this embodiment, the power-down command is assigned to the specialcode and transmitted, as shown in FIG. 12A. The power-down command isdetected by detecting the special code to which the power-down commandis assigned by the decode processing of the command decoder 112 shown inFIG. 8. Occurrence of transfer errors can be reduced by effectivelyutilizing the encoding method. Moreover, transmission and detection ofthe power-down command can be easily realized by current-driving thedifferential signal lines. Furthermore, data transfer can be performedby assigning the special code to the start code or the end code of apacket.

The encoding method performed by the encoding circuit 11 and 31 may beencoding which expands the bit width, and the encoding method is notlimited to the 8B/10B encoding.

11. Power-Down Mode Setting of Clock-Transfer Receiver Circuit

According to this embodiment, the transmitter circuits 22, 24, 46, and48 can separately set the corresponding receiver circuits 42, 44, 26,and 28 to the power-down mode in FIG. 1. Therefore, the power-downcommand for setting the clock-transfer receiver circuit 44 to thepower-down mode or the wakeup voltage for canceling the power-down modemay be transferred through the CLK+/− differential signal lines. Thepower-down command for setting the strobe-transfer (clock transfer in abroad sense) receiver circuit 28 to the power-down mode or the wakeupvoltage for canceling the power-down mode may be transferred through theSTB+/− differential signal lines.

However, as shown in FIG. 13A, the frequency (band) of the signalstransmitted through the CLK+/− and STB+/− differential signal lines ishigher than the frequency of the signals transmitted through the DTO+/−and DTI+/− differential signal lines. Therefore, if the power-downdetection circuit, the power-down setting circuit, and the voltagedriver described in this embodiment are provided on the side of theCLK+/− and STB+/− differential signal lines, transfer performance suchas the transfer rate and transfer reliability may be adversely affected.In particular, if the voltage driver is provided on the side of theCLK+/− and STB+/− differential signal lines, the parasitic capacitanceof the drain terminal or the gate terminal of the transistor may beadded to the differential signal lines, whereby the transfer performancemay be adversely affected.

Therefore, in FIG. 13B, the power-down command for setting theclock-transfer receiver circuit 44 to the power-down mode (hereinaftercalled “clock-transfer power-down command”) and the wakeup voltage forcanceling the power-down mode (hereinafter called “clock-transfer wakeupvoltage”) are transmitted through the OUT-transfer DTO+/− differentialsignal lines.

Specifically, when setting the clock-transfer receiver circuit 44 to thepower-down mode, the OUT-transfer transmitter circuit 22 transmits theclock-transfer power-down command to the OUT-transfer receiver circuit42 through the DTO+/− differential signal lines. The power-down settingcircuit included in the OUT-transfer receiver circuit 42 outputs thepower-down signal to the clock-transfer receiver circuit 44 when theclock-transfer power-down command is detected as the power-down commandtransmitted through the DTO+/− differential signal lines. This causesthe current/voltage conversion circuit and the comparator included inthe clock-transfer receiver circuit 44 to be set to the power-down mode.

When canceling the power-down mode of the clock-transfer receivercircuit 44, the OUT-transfer transmitter circuit 22 (voltage driver)outputs the wakeup voltage to the DTO+/− differential signal lines. Whenthe wakeup detection circuit included in the OUT-transfer receivercircuit 42 detects the wakeup voltage from the OUT-transfer transmittercircuit 22, the wakeup detection circuit outputs a signal for cancelingthe power-down mode of the OUT-transfer receiver circuit 42 and theclock-transfer receiver circuit 44.

The above-described configuration makes it unnecessary to transmit thepower-down command or the wakeup voltage through the CLK+/− differentialsignal lines. Therefore, the transfer performance of the clock transferperformed through the CLK+/− differential signal lines can be preventedfrom being adversely affected.

The power-down command for setting the strobe-transfer receiver circuit26 to the power-down mode or the wakeup voltage for canceling thepower-down mode may be transferred through the IN-transfer DTI+/−differential signal lines. The power-down command for setting theclock-transfer receiver circuit to the power-down mode and thepower-down command for setting the data transfer receiver circuit to thepower-down mode may be commands in different codes or commands in thesame code.

12. Details of Power-Down Control

The details of the power-down control are described below. In thisembodiment, various states are defined as shown in FIGS. 14 and 15. InFIGS. 14 and 15, a device disabled state is a state in which the entireelectronic instrument (host-side data transfer control device andtarget-side data transfer control device) is set to the power-down mode.A target disabled state (period T1) is a state in which the supply ofthe clock signal from the host-side data transfer control device to thetarget-side data transfer control device stops and all the functions ofthe target-side data transfer control device stop. The supply of theclock signal stops after the device has entered the target disabledstate.

An OUT idle state (period T2) is the idle state of the OUT-transfer(transfer from the host-side data transfer control device to thetarget-side data transfer control device) (state between packettransfers). In the OUT idle state, since the host-side transmittercircuit and the target-side receiver circuit are not set to thepower-down mode, the normal transfer can be immediately performed. Sincecurrent constantly flows through these circuits, electric power isconsumed. An OUT-transfer state (period T3) is a state in which theOUT-transfer is performed.

An OUT disabled state (period T4) is a state in which the OUT-transferstops. In this state, the current which has been constantly flowingthrough the host-side transmitter circuit and the target-side receivercircuit is stopped by the power-down mode, whereby a reduction of powerconsumption is realized. The power-down mode can be canceled by allowingthe host-side transmitter circuit to output the wakeup voltage to thetarget-side receiver circuit, whereby the transfer which has stopped canbe resumed.

An IN idle state (period T5) is an idle state of the IN transfer(transfer from the target-side data transfer control device to thehost-side data transfer control device). In the IN idle state, since thetarget-side transmitter circuit and the host-side receiver circuit arenot set to the power-down mode, the normal transfer can be immediatelyperformed. Since current constantly flows through these circuits,electric power is consumed. An IN transfer state (period T6) is a statein which the IN transfer is performed.

An IN disabled state (period T7) is a state in which the IN transferstops. In this state, the current which has been constantly flowingthrough the target-side transmitter circuit and the host-side receivercircuit is stopped by the power-down mode, whereby a reduction of powerconsumption is realized. The power-down mode can be canceled by allowingthe target-side transmitter circuit to output the wakeup voltage to thehost-side receiver circuit, whereby the transfer which has stopped canbe resumed.

In FIG. 14, a “host function” indicates the system function of the host,a “target CLKIN” indicates the presence or absence of the clock input tothe target-side data transfer control device, and a “target function”indicates the system function of the target. A “DTO transmission”indicates the DTO+/− transmission function of the host, and a “DTIreception” indicates the DTI+/− reception function of the host. A “DTItransmission” indicates the DTI+/− transmission function of the target,and a “DTO reception” indicates the DTO+/− reception function of thetarget. A “CLK transmission” indicates the CLK+/− transmission function,and a “CLK reception” indicates the CLK+/− reception function. In FIG.14, a symbol “O” indicates that these functions are in the enabled state(operating state), and a symbol “x” indicates that these functions arein the disabled state (power-down state). A symbol “−” indicates “don'tcare”. In FIG. 15, “S” indicates the start code of packet transfer, and“E” indicates the end code of packet transfer. The start code and theend code are generated by using 8B/10B encoding, for example.

The OUT-transfer is in the idle state at Cl shown in FIG. 15, and apacket is transferred by the OUT-transfer at C2. In the OUT disabledstate at C3, the host-side transmitter circuit and the target-sidereceiver circuit are set to the power-down mode. In the target disabledstate at C4, the supply of the clock signals CLK+/− stops as indicatedby C5, whereby all the functions of the target-side data transfercontrol device stop.

The IN transfer is in the idle state at C6 shown in FIG. 15, and apacket is transferred by the IN transfer at C7. In the IN disabled stateat C8, the target-side transmitter circuit and the host-side receivercircuit are set to the power-down mode. The target disabled state occursat C9. As indicated by C10 and C11, the target supplies the strobesSTB+/− to the host only when performing the normal IN transfer.

According to this embodiment, each transmitter circuit can individuallyset the corresponding receiver circuit to the power-down mode or cancelthe power-down mode. Therefore, the setting and cancellation of thepower-down mode optimum for each state shown in FIGS. 14 and 15 can berealized, whereby a more intelligent power-down control can be realized.

13. Second Configuration Example

A detailed second configuration example of the transmitter circuit andthe receiver circuit in this embodiment is described below using FIG.16. In FIG. 16, the configuration and operation of the circuit blockdenoted by the same symbol as in FIG. 8 are almost the same as those inthe first configuration example shown in FIG. 8. Therefore, descriptionthereof is omitted.

In FIG. 16, the power-down detection circuit 110 includes the commanddecoder 112 and a power-down signal generation circuit 115. The commanddecoder 112 detects the power-down command by the decode processing. Thepower-down signal generation circuit 115 outputs a target sidepower-down signal TPDW at the H level (active) when the power-downcommand is detected.

When the power-down command is detected by the power-down detectioncircuit 110 and the transmitter circuit outputs the power-down voltageto the differential signal lines (DTO+ or DTO−), the power-down settingcircuit 120 sets the current/voltage conversion circuit 90 and thecomparator 100 to the power-down mode. In more detail, the power-downsetting circuit 120 includes an AND circuit AND1. When the target-sidepower-down signal TPDW from the power-down signal generation circuit 115and a host-side power-down signal HPDW, of which the voltage levelchanges corresponding to the state of the differential signal lines, areset at the H level (active), the power-down setting circuit 120 outputsthe power-down signal PD at the H level (active). When the power-downsignal PD is set at the H level, the comparator 100 is set to thedisabled state and the transistors TR3A and TR3B are turned OFF, wherebythe receiver circuit is set to the power-down mode.

The wakeup detection circuit 130 detects cancellation of the power-downmode and outputs the wakeup signal TWUP. In more detail, when the wakeupdetection circuit 130 detects cancellation of the power-down mode afterthe receiver circuit has been set to the power-down mode by thepower-down voltage output to the differential signal lines from thetransmitter circuit, the wakeup detection circuit 130 outputs the wakeupsignal TWUP at the H level (active). When the wakeup signal TWUP is setat the H level, the logic circuit in the subsequent stage (circuit in alayer higher than the physical layer) is awakened.

The operation in the second configuration example shown in FIG. 16 isdescribed below using waveform diagrams shown in FIGS. 17 and 18. Whenthe transmitter circuit transmits the power-down command to the receivercircuit as indicated by Dl shown in FIG. 17, the power-down detectioncircuit 110 detects the power-down command. When the power-down commandis detected, the power-down signal generation circuit 115 outputs thesignal TPDW at the H level as indicated by D2.

The transistor TR2A of the transmitter circuit is turned ON when thesignal PDIN is set at the H level, whereby the voltage driver 70 iselectrically connected with the differential signal lines. When thevoltage driver 70 outputs the power-down voltage at the H level of theCMOS voltage level to the differential signal lines as indicated by D3shown in FIG. 17, the signal HPDW is set at the H level (active) asindicated by D4. Since both the signals HPDW and TPDW are set at the Hlevel, the power-down signal PD output from the power-down settingcircuit 120 is set at the H level as indicated by D5. When the signal PDis set at the H level (active), the comparator 100 is set to thedisabled state and the transistors TR3A and TR3B are turned OFF, wherebythe receiver circuit is set to the power-down mode.

As described with reference to FIGS. 13A and 13B, when the signal PD isset at the H level and the data transfer receiver circuits (42, 26) areset to the power-down mode, it is preferable to set the clock-transferreceiver circuits (44, 28) to the power-down mode. When the power-downmode of the data transfer receiver circuits is canceled, it ispreferable to cancel the power-down mode of the clock-transfer receivercircuits. In this case, the data transfer receiver circuit outputs thesignal PD to the clock-transfer receiver circuit, and the power-downmode of the clock-transfer receiver circuit is set or cancelled based onthe signal PD.

When the signal HPDW is set at the H level, the output nodes NA and NBof the RS flip circuits (NAND1, NAND2) included in the wakeup detectioncircuit 130 are respectively set at the L level and the H level, asindicated by D6 and D7 shown in FIG. 17. In this case, since the node NDof the signal HPDW is at the H level, the wakeup signal TWUP output fromthe wakeup detection circuit 130 remains at the L level (inactive) asindicated by D8.

The signal PDIN is then set at the L level, whereby the transistor TR2Ais turned OFF as indicated by El shown in FIG. 18. This causes thesupply of the power-down voltage to the differential signal lines to bestopped and the power-down mode to be canceled, whereby the differentialsignal lines are set to the idle state as indicated by E2. In the idlestate, since the transistors TR1A and TR1B of the transmitter circuitare turned OFF, the voltage levels of the differential signal lines areset at a low voltage level of about 1 V, for example. Therefore, thesignal HPDW is set at the L level as indicated by E3, and the power-downsignal PD is set at the L level (inactive) as indicated by E4. Thiscauses the comparator 100 to be set to the enabled state and thetransistors TR3A and TR3B to be turned ON, whereby the power-down modeof the receiver circuit is canceled. As described with reference toFIGS. 13A and 13B, the power-down mode of the clock-transfer receivercircuits (44, 28) is also canceled.

The signal HPDW may be set at the L level by causing the transistorsTR1A and TR1B to be turned ON after the transistor TR2A has been turnedOFF. The signal HPDW may be set at the L level by causing the transistorTR2A to be turned ON for a predetermined period and allowing the voltageoutput circuit 72 to output a voltage at the L level in thepredetermined period.

When the node ND of the signal HPDW is set at the L level, since thenode NB and the node NC of the wakeup detection circuit 130 arerespectively set at the H level and the L level, the wakeup signal TWUPis set at the H level as indicated by E5 shown in FIG. 18. The logiccircuit in the subsequent stage (circuit in a layer higher than thephysical layer) is awakened by being triggered by the wakeup signal TWUPset at the H level. When the signal TWUP is set at the H level, thepower-down signal generation circuit 115 sets the signal TPDW at the Llevel after a predetermined period has elapsed as indicated by E6. Thiscauses the voltages of the nodes NA and NB to be respectively set at theH level and the L level as indicated by E7 and E8, and the wakeup signalTWUP returns to the L level.

The difference between the first configuration example described withreference to FIGS. 8, 10, and 11 and the second configuration exampledescribed with reference to FIGS. 16 to 19 is described below.

In the first configuration example, the pulse signal PDPLS is set at theL level after the period TD1 has elapsed after detection of thepower-down command as indicated by A5 shown in FIG. 10. This causes thesignal PD to be set at the H level as indicated by A6, whereby thereceiver circuit is set to the power-down mode.

In the second configuration example, when the power-down command isdetected and the signal TPDW is set at the H level as indicated by D1and D2 shown in FIG. 17, and the transmitter circuit outputs thepower-down voltage at the H level to the differential signal lines asindicated by D3 and D4, the signal PD is set at the H level as indicatedby D5, whereby the receiver circuit is set to the power-down mode.

In the first configuration example, when the transmitter circuit outputsthe wakeup voltage at the L level as indicated by B2 shown in FIG. 11,the signal PD is set at the L level as indicated by B5, whereby thepower-down mode of the receiver circuit is canceled.

In the second configuration example, when the supply of the power-downvoltage to the differential signal lines by the transmitter circuitstops as indicated by E2 shown in FIG. 18, the signal PD is set at the Llevel as indicated by E4, whereby the power-down mode of the receivercircuit is canceled. The wakeup signal TWUP is then set at the H levelas indicated by E5, whereby the higher layer logic circuit in thesubsequent stage is awakened.

Specifically, in the first configuration example, the power-down mode isset merely on condition that the power-down command is detected.Therefore, the delay circuit for setting up the periods TD1 and TD2shown in FIG. 10 is necessary. This is because the holding circuit 122shown in FIG. 8 is reset if the timing at which the differential signallines is set at the H level indicated by A4 shown in FIG. 10 is laterthan the timing at which the pulse signal PDPLS is set at the L levelindicated by A5, whereby the power-down mode is canceled. Since thetransmitter circuit cannot know the signal delay state of the receivercircuit, the timing adjustment becomes complicated if such a delaycircuit is provided, whereby the sequence design becomes difficult.

In the second configuration example, the power-down mode is not set evenif the power-down command is merely detected as indicated by D2 shown inFIG. 17, and the power-down mode is set on condition that thetransmitter circuit outputs the power-down voltage after the power-downcommand has been detected as indicated by D3 and D4. Specifically,preparations for transition to the power-down mode are made on conditionthat the power-down command is detected, and the transition to thepower-down mode occurs on condition that the output of the power-downvoltage is detected. This makes it unnecessary to provide a delaycircuit, which is necessary in the first configuration example, wherebythe timing adjustment can be simplified and the sequence design can befacilitated.

In the second configuration example, the wakeup signal TWUP must remainat the L level at the timing indicated by D8 shown in FIG. 17, and thewakeup signal TWUP must be set at the H level at the timing indicated byE8 shown in FIG. 18. However, the signal HPDW is set at the L level andthe signal TPDW is set at the H level in the period TA1 shown in FIG. 17and the period TA2 shown in FIG. 18. Specifically, the signal state isthe same in the period TA1 and the period TA2. Since the clock signalstops in the period between the timing indicated by D8 shown in FIG. 17and the timing indicated by E5 shown in FIG. 18, the period TA1 and theperiod TA2 must be distinguished only by the signal state.

Therefore, in the second configuration example, the wakeup detectioncircuit 130 having the configuration shown in FIG. 16 is provided.Specifically, in the second configuration example, the period TA1 shownin FIG. 17 and the period TA2 shown in FIG. 18 can be distinguished byallowing the RS flip-flop circuits (NAND1, NAND2) of the wakeupdetection circuit 130 to hold the voltage states of the nodes NA and NB.As described above, the wakeup detection circuit 130 is a circuit whichsets the wakeup signal TWUP at the H level (active) when the voltagelevel of the differential signal lines changes from the power-downvoltage (H level, for example) to another voltage level (1 V, forexample) (when the signal HPDW changes from the H level to the L level)after the power-down command has been detected and the output signalTPDW from the power-down detection circuit 110 has been set at the Hlevel (active). This circuit prevents the wakeup signal TWUP from beingset at the H level at the timing indicated by D8 shown in FIG. 17 andcauses the wakeup signal TWUP to be set at the H level at the timingindicated by E5 shown in FIG. 18.

14. Third Configuration Example

A detailed third configuration example of the transmitter circuit andthe receiver circuit in this embodiment is described below using FIG.19. In FIG. 19, the configuration and operation of the circuit blockdenoted by the same symbol as in FIGS. 8 and 16 are almost the same asthose in the first and second configuration examples shown in FIGS. 8and 16. Therefore, description thereof is omitted.

The third configuration example shown in FIG. 19 differs from the secondconfiguration example shown in FIG. 16 in the configuration of thetransmitter circuit. In more detail, in FIG. 19, the current driver 60(first and second current sources) of the transmitter circuit includesN-type (first conductivity type) transistors TR11A and TR12A and acurrent source IHS. The current driver 60 includes N-type (firstconductivity type) transistors TR11B and TR12B and a current source ILS.

The transistor TR11A is provided between the output node NQA and thecurrent source IHS. In more detail, the input signal DIN+ is input to agate terminal of the transistor TR11A, the output node NQA is connectedwith a drain terminal of the transistor TR11A, and the current sourceIHS is connected with a source terminal of the transistor TR11A. Thetransistor TR12A is provided between the output node NQB and the currentsource IHS. In more detail, the input signal DIN− is input to a gateterminal of the transistor TR12A, the output node NQB is connected witha drain terminal of the transistor TR12A, and the current source IHS isconnected with a source terminal of the transistor TR12A.

The transistor TR11B is provided between the output node NQA and thecurrent source ILS. In more detail, the input signal DIN− is input to agate terminal of the transistor TR11B, the output node NQA is connectedwith a drain terminal of the transistor TR11B, and the current sourceILS is connected with a source terminal of the transistor TR11B. Thetransistor TR12B is provided between the output node NQB and the currentsource ILS. In more detail, the input signal DIN− is input to a gateterminal of the transistor TR12B, the output node NQB is connected witha drain terminal of the transistor TR12B, and the current source ILS isconnected with a source terminal of the transistor TR12B.

The current source IHS is provided between the transistors TR11A andTR12A and the power supply VSS (first power supply). The current sourceIHS is a current source which can generate current (500 μA, for example)greater than that of the current source ILS, and may be formed by atransistor to which a first reference voltage is input at a gateterminal, for example.

The current source ILS is provided between the transistors TR11B andTR12B and the power supply VSS (first power supply). The current sourceILS is a current source which can generate current (100 μA, for example)smaller than that of the current source IHS, and may be formed by atransistor to which a second reference voltage lower than the firstreference voltage is input at a gate terminal, for example.

When the input signal DIN+ becomes active (H level) and the input signalDIN− becomes inactive (L level), the transistors TR11A and TR12B areturned ON and the transistors TR12A and TR11B are turned OFF. Thiscauses a large amount of current (500 μA, for example) to flow throughthe DTO+ signal line and a small amount of current (100 μA, for example)to flow through the DTO− signal line. When the input signal DIN+ becomesinactive (L level) and the input signal DIN− becomes active (H level),the transistors TR11A and TR12B are turned OFF and the transistors TR12Aand TR11B are turned ON. This causes a small amount of current to flowthrough the DTO+ signal line and a large amount of current to flowthrough the DTO− signal line.

FIGS. 20A, 20B, and 20C show specific examples of the inverter circuits(inversion circuits) INV1A and INV1B. In FIG. 20A, the inverter circuitINV1A (INV1B) is formed by N-type (first conductivity type) transistorsTR20 and TR21 connected in series between the power supply VDD and thepower supply VSS. The power supply VDD (second power supply) isconnected with a gate terminal of the transistor TR20, and the inputnode NIA (NIB) is connected with a gate terminal of the transistor TR21.A load resistor may be used instead of the transistor TR20. In FIG. 20B,the inverter circuit INV1A (INV1B) is formed by a P-type (secondconductivity type) transistor TR22 and an N-type (first conductivitytype) transistor TR23 connected in series between the power supply VDDand the power supply VSS. The input node NIA (NIB) is connected withgate terminals of the transistors TR22 and TR23. In FIG. 20C, theinverter circuit INV1A (INV1B) is formed by an operational amplifier OP.A reference voltage VREF is input to a first input (negative side) ofthe operational amplifier OP, and the input node NIA (NIB) is connectedwith a second input (negative side) of the operational amplifier OP.

In FIGS. 8, 16, and 19, the circuit formed by the transistor TR4A (TR4B)and the inverter circuit INV1A (INV1B) functions as a low-impedancegeneration circuit. A specific impedance (ZO) of the DTO+ (DTO−)differential signal lines can be matched with the input impedance of thereceiver circuit by complementing the impedance (Z2) of the resistor RA(RB) to the impedance (Z1) generated by the low-impedance generationcircuit (Z0=Z1+Z2). The length of the differential signal lines or thelike is changed depending on the type of an electronic instrument,whereby the specific impedance of the differential signal lines may bechanged. In this case, it is preferable that the resistor RA (RB) be avariable resistor. This enables the circuit formed by the low-impedancegeneration circuit (circuit consisting of the transistor TR4A and theinverter circuit INV1A or the circuit consisting of the transistor TR4Band the inverter circuit INV1B) and the resistor RA (RB) to function asan impedance adjustment circuit. Therefore, impedance matching can beperformed even if the specific impedance of the differential signallines is changed. The resistor RA (RB) may not be provided when thespecific impedance of the differential signal lines is low and impedancematching can be performed only by the input impedance of thelow-impedance generation circuit, for example.

15. Electronic Instrument

FIG. 21 shows a configuration example of an electronic instrument inthis embodiment. The electronic instrument includes data transfercontrol devices 502, 512, 514, 520, and 530 described in thisembodiment. The electronic instrument includes a baseband engine 500(communication device in a broad sense), an application engine 510(processor in a broad sense), a camera 540 (imaging device in a broadsense), and an LCD 550 (display device in a broad sense). In otherwords, the electronic instrument shown in FIG. 21 includes thetarget-side data transfer control devices 520 and 530, the host-sidedata transfer control device 514 connected with the target-side datatransfer control devices 520 and 530 through a serial bus, and one ormore devices 540 and 550 connected with the target-side data transfercontrol devices 520 and 530 through an interface bus. The electronicinstrument may have a configuration in which some of these sections areomitted. According to this configuration, a portable telephone or thelike having a camera function and a display function of a liquid crystaldisplay (LCD) can be realized. However, the electronic instrument inthis embodiment is not limited to the portable telephone, and may beapplied to various electronic instruments such as a digital camera, PDA,electronic notebook, electronic dictionary, or portable informationterminal.

As shown in FIG. 21, the serial transfer described in this embodiment isperformed between the host-side data transfer control device 502provided to the baseband engine 500 and the target-sidedata-transfer-control-device 512 provided to the application engine 510(graphic engine). The serial transfer described in this embodiment isalso performed between the host-side data transfer control device 514provided to the application engine 510 and the data transfer controldevice 520 including a camera interface circuit 522 or the data transfercontrol device 530 including an LCD interface circuit 532.

According to the configuration shown in FIG. 21, EMI noise can bereduced in comparison with a conventional electronic instrument.Moreover, power consumption of the electronic instrument can be furtherreduced by realizing a reduction of scale and power consumption of thedata transfer control device. In the case where the electronicinstrument is a portable telephone, a serial signal line can be used asa signal line which passes through a connection section (hinge section)of the portable telephone, whereby mounting can be facilitated.

The present invention is not limited to the above-described embodiments.Various modifications and variations are possible. Any term (such asN-type, P-type, VSS, VDD, host-side data transfer control device andtarget-side data transfer control device, strobe, IN transfer and OUTtransfer, baseband engine, application engine, camera, LCD, differentialsignal lines, or PLL circuit) cited with a different term having broaderor the same meaning (such as first conductivity type, secondconductivity type, first power supply, second power supply, device,clock signal, data transfer, communication device, processor, imagingdevice, display device, serial signal line, or clock generation circuit)at least once in this specification and drawings can be replaced by thedifferent term in any place in this specification and drawings.

1. A host-side data transfer control device that performs data transferto a target-side data transfer with a target-side data transfer controldevice, the host-side data transfer control device comprising: anOUT-transfer transmitter circuit that transmits OUT data to anOUT-transfer receiver circuit of the target-side data transfer controldevice; a clock-transfer transmitter circuit that transmits a firstclock signal to a clock-transfer receiver circuit of the target-sidedata transfer control device; an IN-transfer receiver circuit thatreceives IN data from IN-transfer transmitter circuit of the target-sidedata transfer control device; a strobe-transfer receiver circuit thatreceives a strobe to sample the IN data, the strobe-transfer receivercircuit receiving the strobe from a strobe-transfer transmitter circuitof the target-side data transfer control device, the strobe beinggenerated by the target-side data transfer control device based on thefirst clock signal; a power-down circuit that sets one mode from modesincluding a first mode and a second mode; and a second clock signal ofthe target-side data transfer control device being generated accordingto the first clock signal received by the clock-transfer receivercircuit, the second clock signal being stopped in the first mode, andthe clock-transfer transmitter circuit transmitting the first clocksignal at least in the second mode.
 2. An electronic instrumentcomprising: the host-side data transfer control device as defined inclaim 1; and at least one of a communication device, a processor, animaging device, and a display device.
 3. A target-side data transfercontrol device that performs data transfer to a host-side data transfercontrol device, the target-side data transfer control device comprising:an OUT-transfer receiver circuit that receives OUT data from anOUT-transfer transmitter circuit of the host-side data transfer controldevice; a clock-transfer receiver circuit that receives a first clocksignal from a clock-transfer transmitter circuit of the host-side datatransfer control device; an IN-transfer transmitter circuit thattransmits IN data to an IN-transfer receiver circuit of the host-sidedata transfer control device; a strobe-transfer transmitter circuit thattransmits a strobe to sample the IN data, the strobe-transfertransmitter circuit transmitting the strobe generated based on the firstclock signal to a strobe-transfer receiver circuit of the host-side datatransfer control device; a power-down circuit that sets one mode frommodes including a first mode and a second mode; and a second clocksignal of the target-side data transfer control device being generatedaccording to the first clock signal received by the clock-transferreceiver circuit, the second clock signal being stopped in the firstmode, and the clock-transfer transmitter circuit transmitting the firstclock signal at least in the second mode.
 4. The target-side datatransfer control device as defined in claim 3, comprising a strobecontrol circuit that receives the first clock signal received by theclock-transfer receiver circuit, and outputs the strobe to thestrobe-transfer transmitter circuit by performing strobe control.
 5. Thetarget-side data transfer control device as defined in claim 3,comprising a frequency divider circuit that receives the first clocksignal received by the clock-transfer receiver circuit and generates asystem clock signal of the target-side data transfer control device. 6.An electronic instrument comprising: the target-side data transfercontrol device as defined in claim 3; and at least one of acommunication device, a processor, an imaging device, and a displaydevice.
 7. A host-side data transfer control device that performs datatransfer to a target-side data transfer control device, the host-sidedata transfer control device comprising: an OUT-transfer transmittercircuit that transmits OUT data to an OUT-transfer receiver circuit ofthe target-side data transfer control device; a clock-transfertransmitter circuit that transmits a first clock signal to aclock-transfer receiver circuit of the target-side data transfer controldevice; and a power-down setting circuit that sets a power-down modeincluding a first mode and a second mode, a sampling of the OUT databeing carried out according to the first clock signal at the target-sidedata transfer control device, a second clock signal of the target-sidedata transfer control device being generated according to the firstclock signal received by the clock-transfer receiving circuit, thesecond clock signal being stopped in the first mode, and theclock-transfer transmitter circuit transmitting the first clock signalat least in the second mode.
 8. The host-side data transfer controldevice as defined in claim 7, comprising: an IN-transfer receivercircuit that receives IN data from an IN-transfer transmitter circuit ofthe target-side data transfer control device; and a strobe-transferreceiver circuit that receives a strobe for sampling the IN data from astrobe-transfer transmitter circuit of the target-side data transfercontrol device; in the first mode, the power-down setting circuitsetting the OUT-transfer transmitter circuit, the clock-transfertransmitter circuit, the IN-transfer receiver circuit, and thestrobe-transfer receiver circuit to the power-down mode, and, in thesecond power-down mode, the setting circuit setting the OUT-transfertransmitter circuit, the IN-transfer receiver circuit, and thestrobe-transfer receiver circuit to the power-down mode without settingthe clock-transfer transmitter circuit to the power-down mode.
 9. Thehost-side data transfer control device as defined in claim 7,comprising: an IN-transfer receiver circuit that receives IN data froman IN-transfer transmitter circuit of the target-side data transfercontrol device; and a strobe-transfer receiver circuit that receives astrobe for sampling the IN data from a strobe-transfer transmittercircuit of the target-side data transfer control device; the modeincluding a third power-down mode, and in the third mode, the power-downsetting circuit setting the IN-transfer receiver circuit and thestrobe-transfer receiver circuit to the power-down mode without settingthe OUT-transfer transmitter circuit and the clock-transfer transmittercircuit to the power-down mode.
 10. The host-side data transfer controldevice as defined in claim 7, at least one of the OUT-transfertransmitter circuit and the clock-transfer transmitter circuittransmitting a power-down command to a receiver that is one of theOUT-transfer receiver circuit and the clock-transfer receiver circuit ofthe target-side data transfer control device for setting the receiver tothe power-down mode by current-driving a serial signal line that is oneof an OUT-transfer serial signal line and a clock-transfer serial signalline using a current driver in a normal transfer mode.
 11. The host-sidedata transfer control device as defined in claim 7, at least one of theOUT-transfer transmitter circuit and the clock-transfer transmittercircuit including a current driver and a voltage driver, the currentdriver current-driving a serial signal line that is one of anOUT-transfer serial signal line and a clock-transfer serial signal line,the voltage driver electrically disconnecting from the serial signalline in a normal transfer mode, and the voltage driver electricallyconnecting with the serial signal line and voltage-driving the serialsignal line in the power-down mode, and the voltage driver outputting apower-down voltage or a wakeup voltage to the serial signal line, thepower-down voltage being used for setting a receiver that is one of theOUT-transfer receiver circuit and the clock-transfer receiver circuit ofthe target-side data transfer control device to the power-down mode, andthe wakeup voltage being used for canceling the power-down mode of thereceiver.
 12. An electronic instrument comprising: the host-side datatransfer control device as defined in claim 7; and at least one of acommunication device, a processor, an imaging device, and a displaydevice.